Fuel cell system with improved humidifier

Abstract

The fuel cell system (2) comprises a fuel cell stack (4) having an anode (6) and a cathode (8); a cathode supply means (20) arranged to supply a gas containing air and water to the cathode inlet (8a); an air compressor (22) positioned between the cathode supply means (20) and the cathode (8); a first dosing device (42a) configured to inject water upstream of the air compressor (22); a second dosing device (42b) configured to inject water downstream of the air compressor (22); and a heat exchanger (24) positioned upstream of the air compressor (22) and arranged to receive heat from the cooling circuit of the fuel cell stack (4) and / or from the motor of the air compressor (22).

Description

Technical Field

[0001] The present invention relates to a fuel cell system. More precisely, the present invention relates to a fuel cell system for stationary or mobile equipment, a vehicle equipped with such a fuel cell system, and a method for managing such a fuel cell system.

Background Art

[0002] A typical hydrogen-oxygen proton exchange membrane fuel cell (PEMFC) includes an electrolyte solution contained in a proton-conducting membrane disposed between an anode and a cathode, and this assembly generally forms what is commonly referred to as a stack. In a generally known method, a hydrogen-rich gas is fed into the anode and an oxygen-containing gas such as air is fed into the cathode in order to generate power and, as a by-product, generate water at the cathode outlet.

[0003] To achieve good performance of the stack and minimize stack degradation over time, the stack membrane requires appropriate hydration in all states of operation of the fuel cell, such as startup, steady state, dynamic load, and shutdown. The water generated at the cathode outlet can be used to hydrate the stack, but it is necessary to achieve accurate and controlled hydration in order to avoid flooding or insufficient hydration of the membrane, which can both be harmful to the performance of the fuel cell. The oxygen contained in the air stream is a reactant for the reaction formed on the cathode side of the stack, and the air is rich in gaseous water, i.e., water in the form of a gas such as water vapor, at the cathode outlet. Depending on the water concentration, i.e., humidity, temperature, and pressure, at the cathode outlet, the gaseous water can reach a supersaturated state and condensation can occur. Patent Document 1 discloses a fuel cell system provided with means for humidifying the cathode inlet.

[0004] Prior art has shown that a passive humidifier is used in a stack to transfer water from the cathode outlet to the cathode inlet without compromising the oxygen content of the air supplied at the cathode inlet. Such a passive humidifier generally involves a porous membrane that allows for the simultaneous transfer of water in a liquid state and heat.

[0005] While this type of passive humidifier allows for stack humidification, it comes with several drawbacks. Indeed, such passive humidifiers can be costly and are bulky components that can be complex to integrate into fuel cell systems. Furthermore, passive humidifiers generally have a short lifespan because they must withstand high temperatures. While it is possible to connect the humidifier to a supply air cooler to protect it, this involves additional costs and constraints on the additional components to be integrated into the fuel cell system, making it preferable to avoid relying on this component. Additionally, by design, passive humidifiers do not allow for active control of water transfer from the cathode outlet to the cathode inlet, thus failing to achieve adequate stack humidification in certain configurations, making passive humidifiers somewhat inflexible in their implementation. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] German Patent Application Publication No. 102020206156 Specification [Overview of the project] [Problems that the invention aims to solve]

[0007] Considering the above, there is a need for a humidification system for fuel cells that is more accurate than the passive humidifiers of prior art and enables active humidification of the stack. [Means for solving the problem]

[0008] To that end, the present invention provides a fuel cell system for a vehicle, specifically according to claim 1.

[0009] Thanks to the dosing device, highly precise and active water management is possible. The dosing device can be instructed to inject water upstream of the cathode inlet based on the stack parameters and the gas flow of air and water supplied to the cathode inlet. For example, when the gas entering the air compressor is too dry, a first dosing device humidifies the gas to the appropriate humidity. In another example, when the gas leaving the air compressor is too hot, a second dosing device cools the gas to the appropriate temperature. Thus, the dosing device injects a controlled amount of water upstream and downstream of the air compressor so that the gas has the appropriate water concentration, pressure, and temperature for gas entry at the cathode inlet. Furthermore, the dosing device is less bulky than the passive humidifiers of the prior art, making the fuel cell system according to the present invention more compact. In addition, the dosing device has higher temperature tolerance than the passive humidifiers of the prior art, which contributes to improving the lifespan of the fuel cell system.

[0010] Advantageously, the fuel cell system further comprises a control unit configured to control the opening and closing of the first and second administration devices.

[0011] Along with two injection points, one upstream and one downstream of the air compressor, the presence of a control unit allows for further control of active water management by enabling the active setting of the proportion of water supplied upstream and downstream of the air compressor depending on the gas flow parameters, thereby improving the accuracy of active water management.

[0012] Advantageously, the fuel cell system further comprises a cathode water separator located downstream of the cathode outlet and directly or indirectly connected to the first and second dispensing devices.

[0013] This configuration offers the advantage of recovering the liquid water exiting the cathode outlet for further water injection.

[0014] Advantageously, the fuel cell system further comprises an anode water separator located downstream of the anode outlet and directly or indirectly connected to the first and second dispensing devices.

[0015] This configuration offers the advantage of recovering the liquid water exiting the anode outlet for further water injection.

[0016] The phrase "directly or indirectly connected to ~" is intended to mean that other components may or may not be provided between the water separator and the first and second dosing devices.

[0017] Therefore, the fuel cell system provides several sources of water to be supplied to the administration device. According to embodiments of the present invention, buffer water tanks are provided upstream of the administration device and downstream of the cathode water separator and / or anode water separator. This allows the administration device to inject water toward the cathode inlet even if the water separator has not dispensed water for a period of time.

[0018] Preferably, the fuel cell system further comprises a drain valve positioned between the anode water separator and the cathode water separator.

[0019] Therefore, if necessary, the anode water separator can be drained.

[0020] Advantageously, the fuel cell system further comprises a water pump located upstream of the first and second dispensing devices.

[0021] The presence of a water pump facilitates the supply of water to the administration device.

[0022] Preferably, the fuel cell system further includes a heater configured to heat water in the pump.

[0023] Thanks to the heater, first, it is possible to prevent the water in the pump and / or the buffer water tank from freezing, and second, it is possible to melt the water when it freezes.

[0024] Advantageously, the first and second dosing devices each include an injector. The injector makes it possible to create a water spray that facilitates the evaporation of the water.

[0025] According to the present invention, the fuel cell system further includes a heat exchanger disposed upstream of the air compressor. The heat exchanger is arranged to receive heat from the cooling circuit of the fuel cell stack and / or from the motor of the air compressor.

[0026] The heat exchanger can further facilitate the evaporation of the water contained in the gas before the gas is compressed. Thus, while injecting a larger amount of water, it limits the entry of water droplets that may damage the air compressor into the air compressor.

[0027] The air compressor is housed in a casing having an air inlet and an air outlet.

[0028] According to a first embodiment of the present invention, the heat exchanger is disposed upstream of the air inlet of the air compressor and is arranged to receive heat from the cooling circuit of the fuel cell stack and / or from the motor of the air compressor.

[0029] According to a second embodiment of the present invention, the heat exchanger is disposed downstream of the air inlet of the air compressor so as to be integrated into the air compressor casing and is arranged to receive heat from the cooling circuit of the fuel cell stack and / or from the motor of the air compressor.

[0030] Therefore, the heat exchanger accepts heat, which is a byproduct of other components of the fuel cell system, thereby improving the performance of the fuel cell system.

[0031] Advantageously, the fuel cell system further includes a turbine located downstream of the cathode outlet.

[0032] The turbine can recover some of the energy from the gas flow exiting the cathode outlet, thereby improving the performance of the fuel cell system.

[0033] Preferably, the turbine is located on a shaft shared with the air compressor.

[0034] This allows the energy recovered by the turbine to be used by the air compressor, further improving the performance of the fuel cell system.

[0035] Preferably, the fuel cell system further comprises an auxiliary water separator positioned between the cathode outlet and the turbine.

[0036] Auxiliary water separators can reduce the water concentration in the gas flow entering the turbine. This reduces the risk of water droplets in the gas flow damaging the turbine blades.

[0037] According to the present invention, a vehicle equipped with a fuel cell system as described above is also provided.

[0038] The present invention also provides a method for managing a fuel cell system as described above, comprising the steps of opening and closing first and second dosing devices to partially inject water upstream and downstream of an air compressor, and controlling the opening and closing of the first and second dosing devices.

[0039] The present invention also provides a non-temporary computer-readable storage medium for storing computer instructions, wherein the computer instructions, when executed by a computer, cause the computer to perform the method described above, and a computer program product including computer program instructions, wherein the computer program instructions, when executed by a computer, cause the computer to perform the method described above.

[0040] Other features and advantages will become apparent by reading the following description, given as an example of non-limiting illustration, together with the accompanying drawings. [Brief explanation of the drawing]

[0041] [Figure 1] This is a schematic diagram of a fuel cell system according to a first embodiment of the present invention. [Figure 2] This is a schematic diagram of a fuel cell system according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0042] In the following description, the terms "downstream" and "upstream" refer to the circulation directions of various fluids in the fuel cell system, and these directions are depicted by arrows in the diagrams.

[0043] Figure 1 illustrates a fuel cell system 2 according to a first embodiment of the present invention. The fuel cell system 2 is suitable for installation in a vehicle as a power source.

[0044] The fuel cell system 2 comprises a fuel cell stack 4 positioned between the anode 6 and the cathode 8 in a generally known manner, and therefore the basic operation of the stack 4, anode 6, and cathode 8 for generating power will not be described in detail.

[0045] On the anode side, the fuel cell system 2 includes an anode supply means 10 positioned to supply hydrogen-rich gas to the anode inlet 6a, where the hydrogen is, for example, in the form of dihydrogen. The anode supply means 10 may include a suitable tank for storing such hydrogen-rich gas, an example of which is a pressurized tank. Between the anode supply means 10 and the anode inlet 6a, the fuel cell system 2 includes one or more anode valves 12 and a blower 14 for blowing the recirculated gas toward the anode inlet 6a. The recirculated gas is a mixture of hydrogen-rich gas, nitrogen, and water vapor.

[0046] The fuel cell system 2 further includes an anode water separator 16 located downstream of the anode outlet 6b. While some of the hydrogen in the hydrogen-rich gas is consumed by the stack 4 at the anode 6, the gas exiting the anode outlet 6b still contains hydrogen mixed with water and nitrogen. The anode water separator 16 allows for the separation of the gas exiting the anode outlet 6b into a liquid water phase and a gas phase containing hydrogen, water vapor, and nitrogen. The gas phase exits the anode water separator 16 into an anode recirculation duct 18 to reduce hydrogen loss and thereby improve the performance of the fuel cell 2, which then passes through a blower 14 and finally connects to the anode inlet 6a. This also reduces the amount of hydrogen released into the waste of the fuel cell system 2.

[0047] On the cathode side, the fuel cell system 2 includes a cathode supply means 20 positioned to supply an oxygen-containing gas, such as air extracted from the atmosphere, to the cathode inlet 8a. Downstream of the cathode supply means 20, the fuel cell system 2 includes an air compressor 22 for compressing air before it is fed into the cathode inlet 8a. The air compressor 22 is housed in a casing having an air inlet 9a and an air outlet 9b. In this embodiment, a heat exchanger 24 is positioned upstream of the air inlet 9a of the air compressor 22 and configured to heat the air before it enters the air compressor 22, and the heat exchanger 24 is preferably positioned to receive heat from a cooling circuit (not shown in the figure) of the fuel cell stack 4 in order to add value to the heat generated by the fuel cell stack 4.

[0048] The fuel cell system 2 includes a cathode water separator 26 located downstream of the cathode outlet 8b. Water produced at the cathode by a reaction between oxygen from the air and hydrogen ions coming from the anode through the stack is separated from the gas flow exiting the cathode outlet to produce a liquid water phase and a gas phase with a lower water concentration. The gas phase exits the fuel cell system 2 via an exhaust pipe 28. The anode water separator 16 and the cathode water separator 26 are connected by a drain valve 30 configured to allow or prevent the transfer of the liquid phase from the anode water separator 16 to the cathode water separator 26. The anode water separator 16 is also provided with a purge valve 32 configured to allow or prevent the transfer of the hydrogen-containing gas phase from the anode water separator 16 to the exhaust pipe 28 for discharge.

[0049] Between the cathode outlet 8b and the cathode water separator 26, the fuel cell system 2 includes a turbine 34 located downstream of the cathode outlet 8b to recover a portion of the energy of the gas exiting the cathode outlet 8b. The turbine 34 is located on a shaft common to the air compressor 22 so that the energy recovered by the turbine 34 is used to power the air compressor 22. An auxiliary water separator 36 is located upstream of the turbine 34 to reduce the water concentration of the gas fed to the turbine 34 in order to reduce the risk of water droplets damaging the turbine blades. The water recovered by the auxiliary water separator 36 is transferred to the cathode water separator 26 via auxiliary water piping 38, or, according to a variation of this embodiment (not shown), directly to a buffer tank 46 (see below for more details on the buffer tank 46).

[0050] The fuel cell system 2 includes a water recirculation duct 40 positioned to provide water to humidify the cathode inlet 8a. The water recirculation duct 40 includes a first dosing device 42a configured to inject water upstream of the air compressor 22, most preferably upstream of the heat exchanger 24, and a second dosing device 42b configured to inject water downstream of the air compressor 22. The first dosing device 42a and the second dosing device 42b each include an injector suitable for injecting water. The first dosing device 42a and the second dosing device 42b inject water coming from the cathode water separator 26, which may be generated by the cathode water separator 26 itself or by the anode water separator 16 or the auxiliary water separator 36. A water pump 44 is provided in the water recirculation duct 40 to deliver water to the first dosing device 42a and the second dosing device 42b. Furthermore, a buffer tank 46 is provided upstream of the water pump 44 to store water coming from various water separators. To prevent the water from freezing in the water pump 44 and the buffer tank 46, the fuel cell system 2 includes a heater 48, such as an electric heater, which is positioned to heat the water contained in the water pump 44 and the buffer tank 46. The heater 48 may be activated during startup of the fuel cell system 2 to thaw the water contained in the buffer tank 46.

[0051] The fuel cell system 2 includes a control unit 50 connected to the first dispensing device 42a and the second dispensing device 42b to control the opening and closing of the first dispensing device 42a and the second dispensing device 42b. The control unit 50 may also be connected to a heat exchanger 24 to control the amount of heat added to the gas upstream of the air compressor 22.

[0052] The fuel cell system 2 can be controlled as follows: Depending on the parameters of the fuel cell stack 4 and the expected performance of the fuel cell system 2, i.e., the required power output, target parameters for the air supplied to the cathode inlet 8a are determined, most importantly, in terms of temperature, pressure, and water concentration.

[0053] Depending on these target parameters, the control unit 50 actively controls the opening and closing of the first dispensing device 42a and the second dispensing device 42b so that water is injected from the first dispensing device 42a at an active first flow rate, and water is injected from the second dispensing device 42b at an active second flow rate. The water injected by the first dispensing device 42a passes through the heat exchanger 24 to be heated and then through the air compressor 22 before being sent to the cathode inlet 8a. The water injected by the second dispensing device 42b is not heated by the heat exchanger 24 and is not compressed by the air compressor 22.

[0054] Therefore, it is understood that if the pressure or temperature of the air entering the cathode inlet 8a is below its target value, more water should be injected by the first dispensing device 42a. Conversely, if the pressure or temperature of the air entering the cathode inlet 8a is above its target value, more water should be injected by the second dispensing device 42b.

[0055] In practice, the method may involve injecting a certain amount of water by a second dosing device 42b to bring the temperature at the cathode inlet 8a to a target value. Thus, water is injected by the first dosing device 42a to bring the water concentration at the cathode inlet 8a to a target value. The heat supplied to the gas by the heat exchanger 24 upstream of the air compressor 22 is regulated to prevent the presence of water droplets that could damage the air compressor 22.

[0056] Figure 2 illustrates a fuel cell system 2 according to a second embodiment of the present invention. The elements of this fuel cell system 2 according to the second embodiment, which are similar to the elements of the fuel cell system of the first embodiment, share the same reference numerals.

[0057] The fuel cell system 2 in Figure 2 differs from the fuel cell system 2 of the previous embodiment in that the heat exchanger 24' is located downstream of the air inlet 9a of the air compressor 22, so that the heat exchanger 24' is integrated into the housing of the air compressor 22 rather than being a separate component. In this case, the heat exchanger 24' is positioned to receive heat from the cooling circuit of the fuel cell stack 4 (not shown in the figure) and / or from the motor of the air compressor 22 in order to add value to the heat generated by the fuel cell stack 4 and the motor of the air compressor 22. The fuel cell system 2 in Figure 2 operates and is controlled in a similar manner to the fuel cell system of the previous embodiment.

[0058] The embodiments described herein are illustrative and not limiting. Clearly, many improvements and modifications of the present invention are possible in terms of the prior teachings without departing from the concept of the present invention. It should therefore be understood that the present invention can be implemented in ways other than those explicitly described.

[0059] The present invention is applicable to stationary equipment (e.g., power plants) and mobile equipment (e.g., road vehicles such as passenger cars and trucks, railways, ships, aircraft, and spacecraft).

[0060] An additional drain valve may be provided at the outlet of the cathode water separator to transfer water from the cathode water separator to a buffer tank. This drain valve may be opened when the fuel cell system is shut down to prevent the water from freezing in the cathode water separator.

[0061] The heat exchanger may receive heat from some other heat source in the fuel cell system.

[0062] Both the anode water separator and the cathode water separator may be connected individually to the buffer tank. In other words, instead of being arranged in series in the embodiments of Figures 1 and 2, the anode water separator and the cathode water separator may be arranged in parallel with respect to the buffer tank.

[0063] When dealing with freezing conditions, the piping of a fuel cell system may be purged during a shutdown of the fuel cell system to prevent water from freezing in the piping. [Explanation of Symbols]

[0064] 2. Fuel cell system 4. Fuel cell stack 6 Anodes 6a Anode entrance 6b Anode exit 8 Cathode 8a Cathode entrance 8b Cathode exit 9a Air Inlet 9b Air outlet 10 Anode supply means 12 Anode valves 14 Blower 16 Anode water separator 18 Anode recirculation duct 20 Cathode supply means 22 Air compressor 24 Heat exchanger 26 Cathode water separator 28 Exhaust piping 30 Drain valve 32 Purge valve 34 Turbine 36 Auxiliary water separator 38. Auxiliary water piping 40 Water recirculation duct 42a First administration device 42b Second administration device 44 Water pumps 46 buffer tank 48 Heater 50 control units

Claims

1. A fuel cell stack (4) comprising an anode (6) and a cathode (8), A cathode supply means (20) is arranged to supply a gas containing air and water to the cathode inlet (8a), An air compressor (22) is positioned between the cathode supply means (20) and the cathode (8), A first dispensing device (42a) configured to inject water upstream of the air compressor (22), and a second dispensing device (42b) configured to inject water downstream of the air compressor (22), A heat exchanger (24) is positioned upstream of the air compressor (22) and is configured to receive heat from the cooling circuit of the fuel cell stack (4) and / or from the motor of the air compressor (22), A fuel cell system (2) equipped with the following:

2. The fuel cell system (2) according to claim 1, further comprising a control unit (50) configured to control the opening and closing of the first and second administration devices (42a, 42b).

3. The fuel cell system (2) according to claim 1 or 2, further comprising a cathode water separator (26) located downstream of the cathode outlet (8b) and directly or indirectly connected to the first and second dispensing devices (42a, 42b).

4. The fuel cell system (2) according to any one of claims 1 to 3, further comprising an anode water separator (16) located downstream of the anode outlet (6b) and directly or indirectly connected to the first and second dispensing devices (42a, 42b).

5. The fuel cell system (2) according to claim 4, which is dependent on claim 3, further comprising a drain valve (30) disposed between the anode water separator (16) and the cathode water separator (26).

6. The fuel cell system (2) according to any one of claims 1 to 5, further comprising a water pump (44) positioned upstream of the first and second dispensing devices (42a, 42b).

7. The fuel cell system (2) according to claim 6, further comprising a heater (48) configured to heat the water in the pump (44).

8. The fuel cell system (2) according to any one of claims 1 to 7, wherein the first and second administration devices (42a, 42b) each include an injector.

9. The fuel cell system (2) according to any one of claims 3 to 8, further comprising a turbine (34) located downstream of the cathode outlet (8b).

10. The fuel cell system (2) according to claim 9, wherein the turbine (34) is arranged on a shaft common to the air compressor (22).

11. The fuel cell system (2) according to claim 9 or 10, further comprising an auxiliary water separator (36) disposed between the cathode outlet (8b) and the turbine (34).

12. A vehicle comprising a fuel cell system (2) according to any one of claims 1 to 11.

13. A method for managing a fuel cell system (2) according to any one of claims 1 to 11, comprising the steps of opening and closing the first and second dispensing devices (42a, 42b) to partially inject water upstream and downstream of the air compressor (22), and controlling the opening and closing of the first and second dispensing devices (42a, 42b).

14. A non-temporary computer-readable storage medium for storing computer instructions, wherein, when executed by a computer, the computer instructions cause the computer to perform the method described in claim 13.

15. A computer program product comprising computer program instructions, wherein, when executed by a computer, the computer program instructions cause the computer to perform the method described in claim 13.

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