EP4222799A1

EP4222799A1 - Method for managing heat in a vehicle fuel cell system

Info

Publication number: EP4222799A1
Application number: EP21786130.1A
Authority: EP
Inventors: Jurgen Dedeurwaerder
Original assignee: Plastic Omnium Advanced Innovation and Research SA
Current assignee: Plastic Omnium Advanced Innovation and Research SA
Priority date: 2020-09-30
Filing date: 2021-09-28
Publication date: 2023-08-09
Also published as: JP2023546799A; KR20230051314A; FR3114692A1; WO2022069463A1; FR3114692B1; KR102584021B1

Abstract

Disclosed is a method for managing heat in a vehicle power supply system (2) that comprises: - a hydrogen fuel cell, - a plurality of cartridges (16) for storing ammonia, - a circuit (20) for injecting each cartridge (16) into the fuel cell (6), - a circuit (8) for cooling the fuel cell, the circuit containing a heat transfer fluid, and - a heat sink (14), at least one of the cartridges (16) being active and at least one of the cartridges (16) being passive. According to the method, at least one of the following steps is implemented: a) increasing the ammonia pressure inside at least one of the active cartridges, b) circulating, in at least one of the passive cartridges (16), the heat transfer fluid leaving the fuel cell (6), c) increasing the speed of ammonia desorption in one of the active cartridges (16), a portion of the desorbed ammonia being stored in one of the passive cartridges (16).

Description

Title of the invention: Process for thermal management of a vehicle fuel cell system

The invention relates to thermal management on board a vehicle. More particularly, the invention relates to a fuel cell power supply system for a vehicle and to a method for thermal management of such a system.

A motor vehicle comprises drive means, powered by a source of energy, which make it possible to set the vehicle in motion. One of the most common power sources includes an internal combustion engine that runs on fuel. However, the combustion of fuel produces carbon dioxide which pollutes the atmosphere, so it may be preferable to use less polluting energy sources.

It is known to use a fuel cell to replace the internal combustion engine, for example a hydrogen cell. The hydrogen, in the form of dihydrogen, is oxidized by the fuel cell which then produces electricity, to supply the drive means, and heat. Hydrogen can be stored as ammonia gas absorbed in or adsorbed on a salt in storage cartridges. This is a safe method of storing hydrogen. The ammonia must therefore be desorbed from the salt and then be cracked in order to form dihydrogen which can then be supplied to the fuel cell.

For reasons of brevity, in the context of the description of the present invention, the terms absorb and desorb will be used to designate respectively the storage and the release of gaseous ammonia on or from a salt, whether this storage takes place by absorption or adsorption.

A so-called “low temperature” battery works best when it is at a temperature generally between 60°C and 80°C. It is therefore necessary to evacuate the heat generated by the oxidation of dihydrogen so that the temperature of the cell does not exceed this value too much.

To this end, it is known to pass a cooling fluid in contact with the cell in order to absorb heat therefrom, the latter being dissipated by the ambient air by means of a radiator. However, this solution may not be sufficient to maintain the battery at the optimum operating temperature. Indeed, if the temperature of the ambient air is itself high, for example in summer and/or in countries with a hot climate, the temperature difference between the ambient air and the battery means that the radiator cannot not dissipate a large enough amount of heat to keep the battery at its optimum operating temperature. In addition, during phases where the battery must deliver a greater quantity of electrical energy, therefore during which it generates more heat, the radiator may also be insufficient to dissipate this excess heat.

Document WO2011107279 proposes using part of the heat generated by the fuel cell to supply the desorption of ammonia in the storage cartridges, this desorption reaction being endothermic. This makes it possible to have, in addition to the radiator, another source of evacuation of the heat generated by the battery. However, this may still not be enough to keep the battery temperature at optimum operating temperature.

The aim of the invention is in particular to remedy this problem by making it possible to evacuate even more heat from the battery, in particular during a phase of intense use of the latter.

To this end, provision is made according to the invention for a thermal management method in an electrical power supply system for a vehicle, the system comprising:

- a fuel cell capable of being supplied with dihydrogen,

- several ammonia storage cartridges in absorbed form in a matrix,

- an injection circuit connecting an output of each of the cartridges to an input of the stack,

- a cell cooling circuit, in which a heat transfer fluid circulates, comprising branches supplying each of the cartridges, and

- a radiator capable of cooling the heat transfer fluid, in which, at least one of the cartridges occupying an active state in which it releases gaseous ammonia into the injection circuit and at least one of the cartridges occupying a passive state in which it does not release gaseous ammonia into the injection circuit, at least one of the following steps is implemented: a) the ammonia pressure is increased inside at least one of the cartridges occupying the state active, b) circulating the heat transfer fluid leaving the stack in at least one of the cartridges occupying the passive state, c) increasing the ammonia desorption rate in one of the cartridges occupying the active state, part of the desorbed ammonia being stored in one of the other cartridges, preferably in one of the cartridges occupying the passive state.

Thus, heat requirements can be temporarily created within the ammonia storage cartridges. Step a) makes it possible to shift the thermodynamic equilibrium in the cartridge. By allowing an increase in ammonia pressure in the cartridge, we can increase the temperature necessary to reach equilibrium, and therefore the heat requirements of this cartridge. In other words, the temperature in the cartridge is increased by causing it to absorb more heat, which has the effect of increasing, indirectly therefore, the ammonia pressure in the cartridge. Step b) makes it possible to store heat in at least one of the cartridges occupying the passive state without thereby switching it to the active state. Step c) makes it possible to create an excess of ammonia in at least one of the cartridges occupying the active state, relative to the instantaneous consumption of the stack, and therefore an excess of heat consumption for the cartridge concerned.

Each of these steps makes it possible to temporarily increase the heat consumed by the cartridges and therefore to reduce the heat generated by the battery, which must be eliminated by means of the radiator so that the battery remains at a temperature close to the temperature of use. optimal.

Advantageously, at least two of steps a), b) and c) are implemented.

Advantageously, the three steps a), b) and c) are implemented.

It is thus possible to further increase the quantity of heat emitted by the cell which is consumed by the system. This also makes it possible to nimbly modulate the amount of thermal energy that is consumed by the cartridges.

In a specific embodiment, step d) consisting in decreasing the power of the battery is implemented.

Advantageously, in step a), the pressure is increased in at least one of the cartridges occupying the active state to a value greater than 3 bar, preferably greater than 4 bar, preferably greater than 5 bar.

Such an increase in pressure makes it possible to significantly increase the thermodynamic equilibrium temperature in the cartridge. For example, in the case of a calcium chloride matrix, an increase in pressure from 2 bar to 5 bar shifts the equilibrium temperature from about 45°C to 65°C.

Advantageously, the cartridges each comprise a calcium chloride matrix capable of absorbing and desorbing ammonia.

This salt effectively stores ammonia.

More generally, the matrix may be in the form of a salt of general formula M _a (NH ₃ ) nX _z , in which M is one or more cations chosen from alkali metals such as Li, Na, K or Cs, alkaline earth metals such as Mg, Ca or Sr, and/or transition metals such as V, Cr, Mn, Fe, Co, Ni, Cu or Zn or their combinations such as NaAl, KAI, K ₂ Zn, CsCu or K ₂ Fe, X is one or more anions chosen from fluoride, chloride, bromide, iodide, nitrate ions, thiocyanate, sulphate, molybdate and phosphate, a is the number of cations per molecule of salt, z is the number of anions per salt molecule and n is the coordination number, ranging from 2 to 12.

Advantageously, the injection circuit comprises an ammonia cracking module, capable of transforming the ammonia into a gaseous mixture comprising dinitrogen, dihydrogen and ammonia, and, if necessary, a purification module, capable of reduce the ammonia content of the gas mixture.

It is thus possible to supply the cell with a gaseous mixture that is particularly pure in dihydrogen. This makes it possible in particular to make the invention applicable to batteries of the “PEMFC” type, acronym for the Anglo-Saxon terms “Proton Exchange Membrane Fuel Cell”, which need a high level of hydrogen purity to operate.

Advantageously, the method is implemented on board a vehicle.

Provision is also made according to the invention for an electrical power supply system for a vehicle, comprising:

- a fuel cell capable of being supplied with dihydrogen,

- several ammonia storage cartridges in absorbed form in a matrix,

- a cell cooling circuit, in which a heat transfer fluid circulates, comprising branches supplying each of the cartridges,

- a radiator capable of cooling the heat transfer fluid, and

- A control unit capable of implementing a thermal management method as described above.

There is also provided according to the invention a motor vehicle comprising a supply system as described in the foregoing.

Brief description of figures

The invention will now be presented in support of the following description given solely by way of example and made with reference to the appended drawings in which:

[Fig. 1] Figure 1 is a diagram illustrating a vehicle power supply system according to a first embodiment of the invention, and

[Fig. 2] Figure 2 is a diagram illustrating a vehicle power supply system according to a second embodiment of the invention.

detailed description There is shown in Figure 1 an electrical power supply system 2 for a vehicle 4 according to a first embodiment of the invention.

The power system 2 includes a fuel cell 6 of the hydrogen type. More specifically, it may be a cell of the type commonly designated "AMFC", acronym for the Anglo-Saxon terms Alkaline Membrane Fuel Cell, or "PEMFC", acronym for the Anglo-Saxon terms "Proton Exchange Membrane Fuel Cell ". Since these types of battery are known from the state of the art, their operation will not be described in detail in what follows.

The cell 6 is arranged to be supplied with dihydrogen with a view to oxidizing it in order to produce electrical energy, which is transmitted to drive means (not shown) of the vehicle 4. This oxidation reaction being exothermic, it also generates heat which raises the temperature of the battery 6 when it operates.

In order to cool the stack 6, the power supply system 2 comprises a cooling circuit 8 of the stack. This cooling circuit 8 comprises a conduit, in which a heat transfer fluid flows, which passes into contact with the battery 6 so that the heat transfer fluid can exchange heat with the battery 6. The latter has an optimum temperature of use, here of the order of 70° C., at which it reaches maximum efficiency. In order to monitor the temperature of the cell 6, the cooling circuit 8 comprises temperature sensors 10 located upstream and downstream of the cell 6 by considering the direction of circulation of the heat transfer fluid in the cooling circuit 8. The circulation of the heat transfer fluid in the cooling circuit 8 is allowed by means of a pump 12 located at the outlet of the cell 6. The direction of circulation of the heat transfer fluid in the cooling circuit 8 is represented by arrows in FIG.

The supply system 2 comprises a radiator 14 through which the cooling circuit 8 passes. The radiator 14 is exposed to the ambient air, so that the heat transfer fluid passing through the radiator 14 can exchange heat with the air. ambient to cool the heat transfer fluid.

The supply system 2 comprises several storage cartridges 16 each comprising a matrix 18 allowing the storage of gaseous ammonia, which is a precursor of dihydrogen. The ammonia is absorbed in the matrix 18 and can also be adsorbed on the matrix 18. For this purpose, the matrix 18 can consist of a salt, for example calcium chloride. This salt is particularly suitable since one molecule of calcium chloride can form a bond with eight molecules of ammonia.

The power supply system 2 comprises an injection circuit 20 connecting an output of each of the cartridges 16 to an input of the battery 6. The injection circuit 20 has the function of passing the ammonia from the cartridges 16 to the stack 6. At the outlet of each cartridge 16, the injection circuit 20 comprises a temperature sensor 10 capable of measuring the temperature of the ammonia and a non-return valve 21. The non-return valves 21 allow the cartridges 16 having an ammonia pressure greater than the ammonia pressure at the inlet of the injection circuit 20 to desorb ammonia and inject it into the injection circuit 20 .

The injection circuit 20 comprises a metering unit 22 which makes it possible to meter the quantity of ammonia which is conveyed in the direction of the cell 6. A pressure sensor 24 is placed at an inlet of the metering unit 22 in order to measure the pressure of the ammonia entering the dosing unit 22.

The injection circuit 20 comprises a cracking module 26, located downstream of the metering unit 22 considering the direction of circulation of the ammonia in the injection circuit 20, in which the cracking reaction of ammonia. This reaction makes it possible to produce, from ammonia, a gaseous mixture comprising dinitrogen, dihydrogen and ammonia.

The injection circuit 20 comprises a purification module 28, located downstream of the cracking module 26 considering the direction of circulation of the ammonia in the injection circuit 20, capable of reducing the ammonia content of the gaseous mixture. This purification step is critical in particular in the case where the cell is of the “PEMFC” type, this type of cell requiring a supply of particularly pure dihydrogen. At the outlet of the purification module 28, the gaseous mixture is supplied to the cell 6 for the oxidation of the dihydrogen.

The cooling circuit 8 comprises a three-way valve 30 fed by the outlet of the pump 12. The heat transfer fluid leaving the pump 12 is partly directed towards the radiator 14. The other part of the heat transfer fluid is directed towards branches 32 supplying each of the cartridges 16. The branches 32 are arranged so that the cartridges 16 are mounted in parallel. An all-or-nothing valve 34 is provided in each of the branches 32 supplying the cartridges 16, so as to be able to control at any time the cartridges 16 through which the heat transfer fluid must pass. The heat transfer fluid leaving the cartridges 16 is directed by the cooling circuit 8 towards the radiator 14.

The power supply system 2 comprises a control unit 36 capable of controlling the operation of the elements of the power supply system.

We will now describe a process for thermal management of the power supply system 2 which is implemented on board the vehicle by the control unit 36.

In a nominal operating phase, the battery 6 allows the production of approximately 100 kW of electrical power. It has a yield of around 50%, so that it consumes 200 kW of chemical power and additionally produces 100 kW of thermal power in the form of heat. In order to achieve this chemical power, it is necessary to feed the cell with a mass flow of 10.75 g/s of ammonia (which corresponds to a molar flow of 0.63 mol/s). To this end, some of the cartridges 16 occupy an active state in which they release gaseous ammonia into the injection circuit 20, while the remaining cartridges 16 occupy a passive state in which they do not release gaseous ammonia into the injection circuit 16. The desorption of this quantity of ammonia per second requires the consumption of 26 kW of thermal power by the cartridge(s) 16. There therefore remains 74 kW of thermal power to be evacuated, in particular by the radiator 14, in order to avoid a rise in temperature of the battery 6, which could then exceed its optimum operating temperature.

Depending on the temperature of the ambient air, the radiator 14 may not be able to dissipate all of the thermal power to be evacuated. In addition, the vehicle 4 may be required to request greater electrical power from the battery 6, which is accompanied by greater thermal power to be dissipated.

In order to temporarily increase the thermal power dissipated by the supply system 2, the control unit 36 implements at least one of the following operations: a) The ammonia pressure inside at least one is increased. least one of the cartridges 16 occupying the active state. This makes it possible to shift the thermodynamic equilibrium in the cartridge or cartridges concerned. By doing so, the temperature necessary to reach equilibrium is increased, and therefore the heat requirements of this cartridge. In the present case, an increase in pressure from 2 bar to 5 bar (in absolute value) shifts the equilibrium temperature from about 45°C to 65°C. It is thus understood that the cartridge or cartridges concerned need to absorb more heat, emitted by the battery, to maintain this balance. b) The heat transfer fluid leaving the stack 6 is circulated in at least one of the cartridges 16 occupying the passive state. The temperature in the cartridge(s) concerned must then be monitored because it must not exceed a threshold temperature which would make the cartridge(s) active, i.e. ammonia would begin to be desorbed in these cartridges to supply the injection circuit 20. However, before reaching this threshold temperature, the cartridge can absorb a certain amount of thermal energy. d) When possible, the electrical power produced by battery 6 can be reduced. This has the effect of reducing the thermal power produced by the battery 6, and therefore also the thermal power that the radiator 14 must dissipate, and the rest of the thermal power to be dissipated which cannot be dissipated by the radiator 14.

Depending on the thermal power which cannot be dissipated by the radiator 14, one can choose to implement one or two of the operations among operations a) and b), and possibly d) if it is permitted. Moreover, these operations can be implemented during different periods. It is thus understood that the invention allows agile management of the dissipation of the thermal power generated by the battery 6.

There is shown in Figure 2 a power supply system 2 'for a vehicle 4 according to a second embodiment of the invention. Elements similar to those of the first embodiment bear identical reference numerals.

The second embodiment of the invention differs from that of the first embodiment in that the injection circuit 20 comprises, in the direction opposite to the metering unit 22, a recycling circuit 38 whose opening and closing is ensured by an all-or-nothing valve 34 arranged in parallel with the cartridges 16 and controlled by the control unit 36. Downstream of this valve, the recycling circuit 38 comprises a reinsertion branch 40 in each of the cartridges 16, each reinsertion branch 40 comprising a non-return valve 21 arranged to prevent ammonia from leaving the cartridges 16 through the reinsertion branches 40.

System 2' operates in the same way as the system according to the first embodiment. In addition, it allows the implementation of another operation in order to increase the thermal power consumed by the system: c) the ammonia desorption rate is increased in one of the cartridges 16 occupying the active state, a part desorbed ammonia being stored in one of the cartridges 16 occupying the passive state. The excess ammonia thus desorbed passes into the recycling circuit 38 and, by pressure difference, enters the cartridges 16 occupying the passive state through non-return valves 21 of the corresponding reinsertion branches 40.

Operations a) and b), and possibly d), can be implemented simultaneously with operation c) to increase the quantity of thermal power used by the system 2′.

The invention is not limited to the embodiments shown and other embodiments will be apparent to those skilled in the art.

List of references

2; 2': energy supply system

4: vehicle 6: battery

8: cooling circuit

10: temperature sensor

12: pump

14: radiator

16: storage cartridge

18: matrix

20: injection circuit

21: non-return valve

22: dosing unit

24: pressure sensor

26: cracking modulus

28: purification module

30: three-way valve

32: branch

34: on/off valve

36: control unit

38: recycling circuit

40: reintegration branch

Claims

[Claim 1] A method of thermal management in an electrical power system (2; 2') for a vehicle, the system comprising:

- a fuel cell (6) capable of being supplied with dihydrogen,

- several cartridges (16) for storing ammonia in absorbed form in a matrix (18),

- an injection circuit (20) connecting an output of each of the cartridges (16) to an input of the battery (6),

- a cooling circuit (8) of the stack, in which circulates a heat transfer fluid, comprising branches (32) supplying each of the cartridges (16), and

- a radiator (14) capable of cooling the heat transfer fluid, characterized in that, at least one of the cartridges (16) occupying an active state in which it releases gaseous ammonia into the injection circuit (20) and at least one of the cartridges (16) occupying a passive state in which it does not release gaseous ammonia into the injection circuit (20), at least one of the following steps is implemented: a) the pressure is increased in ammonia inside at least one of the cartridges (16) occupying the active state, b) the heat transfer fluid leaving the stack (6) is circulated in at least one of the cartridges (16) occupying the state passive, c) the ammonia desorption rate is increased in one of the cartridges (16) occupying the active state, a part of the desorbed ammonia being stored in one of the other cartridges (16), preferably in one of the cartridges (16) occupying the passive state.

[Claim 2] Method according to the preceding claim, in which at least two of steps a), b) and c) are implemented.

[Claim 3] Process according to any one of the preceding claims, in which the three steps a), b) and c) are carried out.

[Claim 4] Method according to any one of the preceding claims, in which step d) consisting in reducing the power of the battery (6) is also implemented.

[Claim 5] Method according to any one of the preceding claims, in which in step a), the pressure is increased in at least one of the cartridges (16) occupying the active state to a value greater than 3 bar, by preferably greater than 4 bar, preferably greater than 5 bar.

[Claim 6] A method according to any preceding claim, wherein the cartridges (16) each comprise a matrix (18) of calcium chloride capable of absorbing and desorbing ammonia.

[Claim 7] Process according to any one of the preceding claims, in which the injection circuit (20) comprises an ammonia cracking module (26), capable of transforming the ammonia into a gaseous mixture comprising dinitrogen, dihydrogen and ammonia, and a purification module (28), capable of reducing the ammonia content of the gaseous mixture.

[Claim 8] Method according to any one of the preceding claims, carried out on board a vehicle (4).

[Claim 9] Electric power supply system (2; 2') for a vehicle, characterized in that it comprises:

- a fuel cell (6) capable of being supplied with dihydrogen,

- a cooling circuit (8) of the stack, in which circulates a heat transfer fluid, comprising branches (32) supplying each of the cartridges (16),

- a radiator (14) capable of cooling the heat transfer fluid, and

- a control unit (36) capable of implementing a thermal management method according to any one of the preceding claims.

[Claim 10] Motor vehicle (4) comprising a supply system (2; 2') according to the preceding claim.