Fuel cell system and method for removing water from a fuel cell system

Abstract

The present invention relates to a method for removing water from a fuel cell system (1) including a fuel cell stack (2) having an anode section (3) and a cathode section (4), a purge valve (5) downstream of the anode section (3) for controlling the purge pressure of the anode section (3), and a backpressure valve (6) downstream of the cathode section (4) for controlling the backpressure of the cathode section (4), the method comprising the steps of closing the purge valve (5) to increase the purge pressure of the anode section (3) to a predetermined purge pressure target value (AP1), closing the backpressure valve (6) to increase the backpressure of the cathode section (4) to a predetermined backpressure target value (KP1), and subsequently opening the purge valve (5) and the backpressure valve (6) to suddenly reduce the increased purge pressure and the increased backpressure. Furthermore, the invention relates to a fuel cell system (1) and a computer program product (10) for carrying out the method according to the invention, and to storage means on which the computer program product (10) is stored.

Description

Technical Field

[0001] The present invention relates to a fuel cell system and a method for removing water from the fuel cell system. The present invention also relates to a computer program product for performing a purge process in a fuel cell system and a storage means storing the computer program product.

Background Art

[0002] Various methods for removing water from a fuel cell system are known in the prior art. The removal of water is usually carried out within the framework of a purge process, in which the piping section of the fuel cell system is purged using at least one purge fluid, thereby removing residual water. Such a purge process can be carried out during a dedicated purge and drying operation and / or during the power generation operation of the fuel cell system.

[0003] From International Publication No. WO 2017 / 089466, a method for purging a fuel cell system during the power generation operation of the fuel cell system can be read. More precisely, a purge chamber for purging the fuel cell system on the anode side and / or the cathode side is described. When the fuel cell system is used as an electrolyzer, the cathode side can be purged. When the fuel cell system is used for power generation, the anode side can be purged.

[0004] Water remaining in the fuel cell system can cause system failures and problems during startup of the fuel cell system, especially during cold startup. Therefore, in order to avoid icing of the fuel cell system in particular and to prepare for the startup process of the fuel cell system, a purge process is carried out during the purge and drying operation. Such a process is provided especially during cold startup, and thereby it can be part of the cold shutdown procedure. On the anode side, the purge and drying are usually carried out by hydrogen gas with the purge valve open. In contrast, on the cathode side, the purge and drying process is carried out using air. For this purpose, usually a large air flow with low air pressure and low humidity is supplied to the cathode side. The purge and drying process is often carried out until a significant decrease in the high-frequency membrane resistance (HFR) can be confirmed. While this requires corresponding measurement techniques, measurement errors can lead to undesirable drying of the membrane. If dried excessively, mechanical stress occurs in the electrolyte membrane, and the life of the membrane may be shortened. Therefore, it is desirable to minimize the drying of the electrolyte membrane and accelerate the entire drying process.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem of the present invention is to take into account at least partially the above problems. In particular, the problem of the present invention is to provide a method for promoting and / or effectively removing water from the fuel cell system together with the fuel cell system. Further, it is an object to provide a computer program product for executing such a method and a storage means in which such a computer program product is stored.

Means for Solving the Problems

[0007] The above problems are solved by the claims. In particular, the above problems are achieved by the method according to claim 1, the fuel cell system according to claim 7, the computer program product according to claim 9, and the storage means according to claim 10. Further advantages of the present invention will become apparent from the dependent claims, the following description and the drawings. In that case, the features and details described in connection with the method are of course also applicable in connection with the fuel cell system according to the present invention, the computer program product according to the present invention, the storage means according to the present invention, and vice versa, and thereby always refer to each other, or can refer to each other, with respect to the disclosure of the individual aspects of the present invention.

[0008] According to a first aspect of the present invention, there is provided a method for removing water from a fuel cell system comprising a fuel cell stack having an anode part and a cathode part, a purge valve downstream of the anode part for controlling the purge pressure of the anode part, and a back pressure valve downstream of the cathode part for controlling the back pressure of the cathode part. The method includes the following steps. a) increasing the purge pressure of the anode part to a predetermined purge pressure target value; b) increasing the back pressure of the cathode part to a predetermined back pressure target value, and then c) abruptly reducing the increased purge pressure and the increased back pressure by opening the purge valve and the back pressure valve.

[0009] That is, according to the present invention, the internal volumes within and around the fuel cell stack in the fuel cell system are first pressurized by respective pressurizations and then rapidly released by opening the valves together. In conventional purge and / or drying methods, there is a relatively constant and stoichiometric pressure in the internal volume in question, or the pressure changes only relatively slowly even if the purge process is impulsive. The impulsive purge process is generated, for example, by a compressor (air supply) or a pressure valve (hydrogen supply). By the method according to the present invention, a rapid release can occur, that is, a (negative) pressure pulse can be generated, and this pressure pulse brings about a much higher flow rate and corresponding maximum shear force than has been possible or efficiently achievable heretofore. Thereby, water, especially in liquid form, that has entered various piping sections and / or functional components such as humidifiers, shut-off valves, and / or outlet valves of the fuel cell system can be effectively discharged from there to the periphery of the fuel cell system. Therefore, the drying and / or purge time of the fuel cell system can be significantly shortened.

[0010] In accordance with step C), while opening the purge valve and the backpressure valve, it is possible to open the drain valve on the anode side in some cases. Thereby, it becomes possible to achieve a faster release, but it is important that the maximum hydrogen release is not exceeded during the purge process.

[0011] The method according to the present invention corresponds to the "inflation" or pressurization and release of the internal volume included in the system. In a PEM system in the automotive sector, the cathode path from the compressor to the backpressure valve may contain, for example, an air volume exceeding 5 liters. The compressed air can have a large amount of energy accordingly. That is, the purge or drying process according to the present invention is achieved rather by suddenly releasing the system than by introducing a fluid. Thereby, the energy stored in the fluid pressure can be converted into a purge shock with a temporarily high air velocity in a short time, and water can be effectively and quickly removed from the fuel cell system.

[0012] The desired pressure increase can be carried out by at least one compressor of the fuel cell system. This can be achieved at the minimum load point or another low load point of the fuel cell system. Subsequently, a conventional drying process can be carried out.

[0013] The purge pressure target value can correspond to the nominal system pressure or the operating pressure, or the operating pressure value when the fuel cell system is in power generation operation. That is, the purge pressure and / or the back pressure can be increased to the nominal operating pressure or substantially the nominal operating pressure.

[0014] This method is particularly carried out after the fuel cell vehicle, especially the fuel cell vehicle including the fuel cell system, has stopped. Thereby, it is possible to prevent harmful ice that may impair the functions of various components of the fuel cell system from being formed in the fuel cell system at an ambient temperature below 0°C.

[0015] The purge valve can be arranged immediately downstream of the anode part. Similarly, the back pressure valve can also be arranged immediately downstream of the cathode part. Nevertheless, additional functional components, especially additional valve units, can be arranged in the flow direction between each electrode part and the purge valve or the back pressure valve. It is advantageous if the valve present on the anode side anyway is used for the purge process.

[0016] As already described above, the abrupt reduction of the increased pressure can be resolved as the abrupt reduction caused by opening the purge valve and the back pressure valve. Closing the valve, or the valve being closed, can be understood as that the flow of the fluid through the fluid pipe where the valve is arranged is blocked, or is substantially blocked, and the valve is in a shut-off position. Opening the valve, or the valve being open, can be understood as that the flow of the fluid through the fluid pipe where the valve is arranged is enabled, or the fluid pipe for the fluid flow is at least released in the region of each valve, or the valve is in a released passage position.

[0017] Steps a) and b) are preferably carried out simultaneously or substantially simultaneously. Thereby, the stress on the electrolyte membrane between the anode part and the cathode part can be prevented. In order to abruptly reduce the increased purge pressure and the increased back pressure, for the same reason, the purge valve and the back pressure valve are preferably also opened simultaneously or substantially simultaneously.

[0018] In a further embodiment of the present invention, in the method, steps a), b) and c) can be continuously carried out several times to remove water from the fuel cell system. That is, the internal volume within and in contact with the anode part and the internal volume within and in contact with the cathode part are pressurized and released at regular intervals. Thereby, water can be removed from the fuel cell system particularly effectively. In experiments within the scope of the present invention, surprisingly, it has been found that this method does not pose a risk of damaging the functional components of the fuel cell system. Rather, due to the high impact strength of the process fluid used, water can be purged from the fuel cell system quickly, surely, and without damaging the components.

[0019] Furthermore, in the method according to the present invention, it is possible to increase the purge pressure of the anode part to the maximum allowable or substantially maximum allowable purge pressure of the anode part, and increase the back pressure of the cathode part to the maximum allowable or substantially maximum allowable back pressure of the cathode part. Thereby, for the impact of the fluid shock for purging or drying the fuel cell system, a correspondingly large value can be achieved without the need to fear damage or destruction of the fuel cell system. Increasing the purge pressure of the anode part to the maximum allowable or substantially maximum allowable purge pressure of the anode part can be understood as increasing the purge pressure to the maximum value of the purge pressure corresponding to the maximum allowable system pressure or operating pressure of the anode part during power generation. Increasing the back pressure of the cathode part to the maximum allowable or substantially maximum allowable back pressure of the anode part can be understood as increasing the back pressure to the maximum value of the back pressure corresponding to the maximum allowable system pressure or operating pressure of the cathode part during power generation.

[0020] In a further embodiment of the present invention, in the method, it is possible to increase the purge pressure of the anode part and the back pressure of the cathode part to values of 2 bar to 5 bar, respectively. These values or these values have been found to be particularly suitable for realizing a purge process that is effective but does not damage the components in the experiments within the scope of the present invention. However, the pressure may be higher or lower. In the method according to the present invention, it may be more advantageous to increase the purge pressure of the anode part and the back pressure of the cathode part to the same value or substantially the same value. Thereby, the method can be carried out, especially without damaging the membrane. In particular, in this case, it should be noted that the back pressure and the purge pressure during the increase to their respective target pressures or maximum pressures are always the same or substantially the same, or there is no significant difference. However, due to the maximum hydrogen release in the exhaust path (usually less than 8% by volume), it may also be necessary to release the cathode pressure faster than the anode pressure. This is particularly advantageous when the opening cross-sectional area of the purge valve is smaller than that of the back pressure valve on the cathode side.

[0021] In fact, furthermore, it has been found that it is also advantageous when the desired back pressure or the corresponding cathode pressure is adjusted by a compressor with the back pressure valve closed and the purge pressure or the corresponding anode pressure follows this back pressure. In this case, for safety technical reasons, it can be noted that, for example, the purge pressure in the form of hydrogen pressure is adjusted or controlled to be always at a minimum and slightly higher, for example, 100 mbar higher than the cathode part in the anode part.

[0022] Furthermore, in the method according to the present invention, the fuel cell system can be operated in a power generation operation for power generation and a purge and drying operation for purging and drying the fuel cell system, and steps a), b) and c) can be executed during the purge and drying operation. That is, this method is preferably performed only during the purge and drying operation as much as possible and should not be performed during the power generation operation of the fuel cell system. In other words, the steps according to the present invention are preferably executed separately from the power generation operation. Thereby, the power generation operation remains unaffected. During the purge and drying operation, the fuel cell system can be operated at the minimum load point of the fuel cell system or another low load point. Immediately after both sides of the vehicle are purged, a voltage is applied to the fuel cell stack. However, since the fuel cell stack is damaged at the open circuit voltage (OCV) without current load, it is advantageous to approach at least the minimum load point, that is, the larger the cell voltage drops below about 0.85 VDC, the larger the amount of current drawn.

[0023] According to a further aspect of the present invention, there is provided a fuel cell system including a fuel cell stack having an anode part and a cathode part, a purge valve downstream of the anode part for controlling the purge pressure of the anode part, and a back pressure valve downstream of the cathode part for controlling the back pressure of the cathode part. The fuel cell system further includes a controller having a pressure increasing unit for closing the purge valve to increase the purge pressure of the anode part to a predetermined purge pressure target value and for closing the back pressure valve to increase the back pressure of the cathode part to a predetermined back pressure target value, and a pressure reducing unit for suddenly, particularly rapidly reducing the increased purge pressure and the increased back pressure by opening the purge valve and the back pressure valve.

[0024] Therefore, the fuel cell system according to the present invention provides the same advantages as those described in detail with reference to the method according to the present invention. This can be ensured in particular by the fact that the pressure increasing unit and the pressure reducing unit are configured and designed to perform the method described in detail above.

[0025] Furthermore, within the scope of the present invention, when a computer program product is executed by a computer, a computer program product including instructions for causing the computer to execute the above method is proposed. For this purpose, storage means storing the computer program product according to this embodiment is provided. The storage means may be provided in the form of a controller in which the computer program product is installed. Therefore, the computer program product and the storage means also bring the above advantages in the same manner. The controller can be understood as a computer or can have a computer for executing the computer program product.

[0026] The computer program product can be implemented as computer-readable instruction code in any suitable programming language such as, for example, JAVA, PYTHON, C++, and / or C#. The computer program product can be stored in a computer-readable storage medium such as a data disk, a removable drive, a volatile or non-volatile memory, or a built-in memory / processor. The instruction code can program a computer or other programmable device such as a controller so that the desired function is executed. Furthermore, the computer program product can be provided on a network such as the Internet or may be provided thereon, from which the user can download it as needed. The computer program product can be realized or can be realized not only by a computer program, that is, software, but also by one or more special electronic circuits, that is, hardware, or in any hybrid form, that is, by software components and hardware components.

[0027] Still other measures for improving the present invention will become apparent from the following description of various embodiments of the present invention schematically shown in the figures.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0029] In FIG. 1, a fuel cell system 1 is schematically shown in the form of a PEM system. The fuel cell system 1 includes a fuel cell stack 2 having an anode part 3, a cathode part 4, and an electrolyte membrane 15 disposed between the anode part 3 and the cathode part 4. The fuel cell system 1 further includes a purge valve 5 downstream of the anode part 3 for controlling the purge pressure of the anode part 3, a back pressure valve 6 downstream of the cathode part 4 for controlling the back pressure of the cathode part 4, and a controller 7. The controller 7 has a pressure increasing unit 8 for increasing the purge pressure of the anode part 3 to a predetermined purge pressure target value AP1 shown in FIG. 2 by closing the purge valve 5, and for increasing the back pressure of the cathode part 4 to a predetermined back pressure target value KP1 shown in FIG. 2 in the same manner by closing the back pressure valve 6. Further, the controller 7 has a pressure reducing unit 9 for suddenly reducing the increased purge pressure and the increased back pressure by opening the purge valve 5 and the back pressure valve 6. The embodiment shown in FIG. 1 further includes a fuel source 11 in the form of a hydrogen tank and a control valve 12 for metering the supply of hydrogen to the injector ejector 13 of the fuel cell system 1. The injector ejector 13 is formed upstream of the anode part 3 to supply fuel to the anode part 3. The anode exhaust gas in the form of a secondary fluid can be sucked in from the injector ejector 13 through the recirculation path 16 and supplied again to the anode part 3. A compressor 14 for feeding air to the cathode part 4 and pressurizing the cathode part 4 is disposed upstream of the cathode part 4. In addition to the illustrated functional components, the fuel cell system 1 can further include BOP components such as a heat exchanger, a humidifier, and / or additional switching valves.

[0030] A computer program product 10 is installed in the controller 7, and this computer program product includes instructions for causing the controller 7 to execute a method for removing water from the fuel cell 1 shown in FIG. 1, which will be described below, when the computer program product 10 is executed by the controller 7.

[0031] Next, this method will be described with reference to FIGS. 2 and 3. In the first step S1, first, the purge valve 5 is closed, and the purge pressure of the anode part 3 is increased to a purge pressure target value AP1 corresponding to a substantially maximum allowable system pressure of about 3 bar in the illustrated example.

[0032] In the second step S2, the back pressure valve 6 is closed, and the back pressure of the cathode part 4 is increased to a back pressure target value KP1 corresponding to a substantially maximum allowable system pressure of, for example, about 3 bar or about 2.5 bar in the illustrated example. At this time, the back pressure is always kept about 100 mbar lower than the purge pressure. In the third step S3, the purge valve 5 and the back pressure valve 6 are opened in order to suddenly or rapidly reduce the increased purge pressure and the increased back pressure to the ambient pressure or a substantially ambient pressure. This can be recognized from the steep drop of the pressure profile A1 of the anode part 3 and the steep drop of the pressure profile K1 in the cathode part 4 after reaching their respective maximum target values AP1 or KP1 in FIG. 2. As shown in FIG. 2, the procedure described in FIG. 3 is repeated two more times, and of course, additional repetitions are also possible. The method described with reference to FIGS. 2 and 3 is executed during the purge and dry operation of the fuel cell system 1.

[0033] In addition to the illustrated embodiments, the present invention enables further design principles. That is, the present invention should not be regarded as being limited to the embodiments described with reference to the figures.

Explanation of Reference Numerals

[0034] 1 Fuel cell system 2 Fuel cell stack 3 Anode part 4 Cathode section 5 Purge valve 6 Backpressure valve 7 Controller 8 Boost unit 9 Pressure reducing unit 10 Computer program product 11 Fuel source 12 Control valve 13 Injector ejector 14 Compressor 15 Electrolyte membrane 16 Recirculation path A1 Pressure profile of the anode section AP1 Purge pressure target value (maximum purge pressure) K1 Pressure profile of the cathode section KP1 Backpressure target value (maximum backpressure)

Claims

1. A method for removing water from a fuel cell system comprising a fuel cell stack having an anode part and a cathode part, a purge valve downstream of the anode part for controlling the purge pressure of the anode part, and a back pressure valve downstream of the cathode part for controlling the back pressure of the cathode part, the method comprising: a) closing the purge valve and increasing the purge pressure of the anode part to a predetermined purge pressure target value (AP1); b) closing the back pressure valve and increasing the back pressure of the cathode part to a predetermined back pressure target value (KP1), and subsequently, c) suddenly reducing the increased purge pressure and the increased back pressure by opening the purge valve and the back pressure valve, wherein the fuel cell system is operated in a power generation operation during power generation, wherein the fuel cell system is operated in a purge and drying operation at a low load point when purging and drying the fuel cell stack, and steps a), b) and c) are carried out during the purge and drying operation, a method in which the back pressure and the purge pressure, each increasing to a target value or a maximum value of pressure, are always kept the same.

2. The method according to claim 1, characterized in that steps a), b) and c) are continuously carried out several times to remove water from the fuel cell system.

3. The method according to claim 1 or claim 2, characterized in that the purge pressure of the anode part is increased to the maximum allowable or substantially maximum allowable purge pressure of the anode part, and the back pressure of the cathode part is increased to the maximum allowable or substantially maximum allowable back pressure of the cathode part.

4. The method according to any one of claims 1 to 3, characterized in that the purge pressure of the anode part and the back pressure of the cathode part are each increased to a value of 2 bar to 5 bar.

5. The method according to any one of claims 1 to 4, characterized in that the purge pressure of the anode part and the back pressure of the cathode part are increased to the same value or a substantially same value.

6. The method according to any one of claims 1 to 5, characterized in that steps a) and b) are carried out using at least one compressor at a low load point.

7. A fuel cell system, comprising a fuel cell stack having an anode part and a cathode part, A purge valve downstream of the anode part for controlling the purge pressure of the anode part, A back pressure valve downstream of the cathode part for controlling the back pressure of the cathode part, A pressure increasing unit for closing the purge valve to increase the purge pressure of the anode part to a predetermined purge pressure target value (AP1), and for closing the back pressure valve to increase the back pressure of the cathode part to a predetermined back pressure target value (KP1); and a pressure reducing unit for suddenly reducing the increased purge pressure and the increased back pressure by opening the purge valve and the back pressure valve, a controller (7) having the same, The fuel cell system is operated in a power generation operation during power generation, The fuel cell system is operated in a purge and drying operation at a low load point when purging and drying the fuel cell stack, A fuel cell system in which the back pressure and the purge pressure, each increasing to a target value or a maximum value of pressure, are always kept the same.

8. The pressure increasing unit and the pressure reducing unit are, a) a step of closing the purge valve to increase the purge pressure of the anode part to a predetermined purge pressure target value (AP1); b) a step of closing the back pressure valve to increase the back pressure of the cathode part to a predetermined back pressure target value (KP1); and subsequently, c) a step of suddenly reducing the increased purge pressure and the increased back pressure by opening the purge valve and the back pressure valve, configured and designed to execute a method including the steps, The fuel cell system according to claim 7, wherein the steps a), b) and c) are executed during the purge and drying operation.

9. A computer program comprising instructions for causing a computer to execute the method according to any one of claims 1 to 6 when the computer program is executed by the computer.

10. A non-transitory computer-readable storage medium storing the computer program according to claim 9.

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