Method for operating a fuel cell system and fuel cell system
By branching off a cooling path for the storage tank downstream of the turbine and using significantly cooled air or exhaust gas to cool the storage tank system, the pre-cooling and flow limitation problems during hydrogen refueling of fuel cell systems are solved, resulting in shorter refueling time and lower costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2024-12-06
- Publication Date
- 2026-07-31
AI Technical Summary
Existing fuel cell systems require pre-cooling and flow restrictions when refueling with hydrogen, resulting in high costs and long refueling times.
By branching off a cooling path for the storage tank downstream of the turbine, the storage tank system is cooled using significantly cooled air or exhaust, eliminating the need for pre-cooling and reducing flow restrictions. Air-to-air or air-to-liquid heat exchangers are then used to further cool the air or exhaust.
It shortens refueling time, reduces the cost of hydrogen supply at hydrogen refueling stations, and improves the efficiency and safety of fuel cell systems.
Smart Images
Figure CN122498026A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for operating a fuel cell system. Furthermore, the invention also relates to a fuel cell system suitable for performing or operable according to this method.
[0002] The preferred application areas of this invention are mobile fuel cell systems or fuel cell vehicles. Background Technology
[0003] Hydrogen-based fuel cell systems are considered a future mobility solution because they emit only water as exhaust and offer rapid refueling. Air and hydrogen are supplied through a subsystem for the electrochemical reactions in the fuel cell. Waste heat generated during the electrochemical reactions is dissipated via a cooling circuit and released into the environment through the vehicle's radiator.
[0004] In practice, a large number of fuel cells are stacked and connected to form a fuel cell stack, also known as a fuel cell pile. To increase power, a fuel cell system may also include more than one stack. This involves a multi-stack system.
[0005] The hydrogen required for the electrochemical reaction is stored in a tank system with one or more compressed gas containers, for example, at a pressure of 700 bar. The compressed gas containers are heated during refueling. To prevent exceeding a pre-defined temperature threshold of, for example, 85°C, the hydrogen is typically pre-cooled to, for example, -40°C at the refueling station. Alternatively or additionally, the flow rate during refueling may be limited.
[0006] Because precooling hydrogen at hydrogen refueling stations is costly and flow restrictions during refueling result in long refueling times, this invention aims to achieve the following technical task: to provide a tank cooling system that does not have these disadvantages.
[0007] This task is accomplished by the method having the features of claim 1 and the fuel cell system having the features of claim 7. Advantageous extensions of the invention can be found in the corresponding dependent claims. Summary of the Invention
[0008] A method for operating a fuel cell system is proposed, the system comprising at least one fuel cell stack having a cathode and an anode. During normal operation of the fuel cell system, air is supplied to the cathode via a supply path, the air having been previously compressed by at least one air compressor integrated in the supply path. Exhaust gas from the cathode is supplied via an exhaust path to a turbine integrated in the exhaust path and operatively connected to the air compressor. During normal operation, hydrogen gas from a storage tank system having at least one compressed gas container is also supplied to the anode. According to the invention, the storage tank system is cooled before, during, and / or after refueling, wherein air or exhaust gas is used for cooling, branching off from the exhaust path downstream of the turbine by an open valve and supplied to the storage tank system via a storage tank cooling path.
[0009] In the proposed method, cooling of the tank system is achieved by depressurizing and thus significantly cooling the air or exhaust gas. This is because the air or exhaust gas is depressurized within the turbine. Depressurization, or expansion, causes a significant drop in temperature (expansion cooling). For example, in a conventional turbine with an efficiency of 65% and the gas expanding from 4 bar to 1 bar, the exhaust gas can be cooled from 30°C to -35°C.
[0010] The primary task of a turbine integrated into the exhaust path is to recover a portion of the energy used for compressed air. The proposed method allows for the integration of another function into the turbine. Air or exhaust gas, significantly cooled by expansion cooling within the turbine, can be branched and delivered to a storage tank system for further cooling. Cooling via the proposed tank system eliminates flow restrictions during refueling, thereby reducing refueling time. Where possible, it can even eliminate the need for pre-cooling of hydrogen at the refueling station, thus reducing the cost of hydrogen supply.
[0011] The proposed method can be performed before, during, and / or after the filling of the tank system. For example, it can be performed shortly before the filling process is initiated. Preferably, the tank system is cooled by expansion cooling at least during filling. More preferably, cooling continues for a period of time after filling to reliably avoid exceeding a predetermined temperature threshold.
[0012] In an extended embodiment of the invention, the at least one fuel cell stack is cooled by a cooling system comprising a cooling circuit with a coolant pump for delivering coolant and a main cooler. This cooling system can be used to initially cool the air or exhaust gas in the at least one fuel cell stack before, during, and / or after refueling the storage system. The cooling system preferably operates such that the coolant in the cooling circuit reaches ambient temperature or near ambient temperature in the main cooler by releasing heat to the environment. Additionally, the delivery power of the coolant pump can be increased. Subsequently, the thus cooled coolant flows into the at least one fuel cell stack and also cools it to ambient temperature or near ambient temperature.
[0013] Preferably, the air or exhaust gas used to cool the storage tank system is first compressed by at least one air compressor and then cooled by a cooler integrated downstream of the air compressor in the air supply path. This compression provides a specific air mass flow rate or exhaust gas mass flow rate. Since the air heats up significantly during compression, it is subsequently cooled by the downstream cooler. Preferably, the at least one air compressor is operated such that a high compression ratio of, for example, 4 to 5, and a high air mass flow rate of, for example, 150 g / s are achieved.
[0014] Furthermore, preferably, a heat exchanger integrated into the air supply path is used as a cooler. This heat exchanger can be circulated by the coolant from the cooling system or by exhaust gas from the exhaust path. Therefore, cooling of the compressed air in the air supply path can be achieved in different ways. Depending on the cooling method, the heat exchanger can be implemented as a gas-liquid heat exchanger or a gas-gas heat exchanger.
[0015] According to a first preferred embodiment of the invention, the cooler is implemented as a gas-to-gas heat exchanger, through which air flows in the supply path on one side and exhaust gas flows in the exhaust path on the other. Preferably, the air compressed by the at least one air compressor is first cooled in the gas-to-gas heat exchanger, and then second cooled in the at least one fuel cell stack by means of a cooling system. Subsequently, the exhaust gas leaving the fuel cell stack preferably has a temperature close to ambient temperature. Using this exhaust gas, the compressed air in the supply path can be cooled in the gas-to-gas heat exchanger, so that the exhaust gas entering the turbine has a temperature slightly higher than ambient temperature. In the turbine, the exhaust gas is then cooled to a temperature of, for example, -30 to -35°C due to expansion.
[0016] According to another preferred embodiment of the invention, the cooler is implemented as a gas-liquid heat exchanger, through which air flows in the gas supply path on one side and coolant flows in the cooling circuit on the other. With the help of the coolant guided through this heat exchanger, the air can be cooled to or near ambient temperature, thus eliminating the need to guide air through the at least one fuel cell stack.
[0017] Therefore, as a further extension, it is proposed that air used for cooling the tank system is introduced from the supply path into the exhaust path via a bypass path that bypasses the at least one fuel cell stack and has an integrated bypass valve, by opening the bypass valve and closing the shut-off valve arranged in the supply path. Air is delivered radially to the turbine via the bypass path instead of being exhausted. This air is also pre-compressed by the at least one air compressor and cooled by a cooler integrated in the supply path downstream of the at least one air compressor, and then introduced into the exhaust path upstream of the turbine via the bypass path.
[0018] Preferably, the tank system and / or at least one temperature-critical component of the tank system directly faces the air or exhaust in the tank cooling path.
[0019] Alternatively, air or exhaust in the tank cooling path is directed through a heat exchanger integrated into the tank system.
[0020] In addition, fuel cell systems proposed to address the aforementioned tasks include: -At least one fuel cell stack with a cathode and an anode, - An air system for supplying air to the cathode of the at least one fuel cell stack, wherein the air system has a supply path and an exhaust path, the supply path having at least one air compressor integrated therein, and the exhaust path having a turbine integrated therein and operatively connected to the air compressor. - A tank system having at least one compressed gas container for storing hydrogen.
[0021] According to the present invention, downstream of the turbine, a storage tank cooling path branches off from the exhaust path, through which air or exhaust gas can be delivered to the storage tank system for cooling.
[0022] The proposed fuel cell system is particularly suitable for carrying out, or operating according to, the methods of the present invention described above. Therefore, the proposed fuel cell system achieves the same advantages. In particular, refueling time can be shortened by eliminating flow restrictions during refueling in the storage tank system. Furthermore, the cost of supplying hydrogen at hydrogen refueling stations can be reduced because, in some cases, the pre-cooling process can be omitted.
[0023] According to a preferred embodiment of the invention, a valve, such as a two-position three-way valve, is integrated into the exhaust path downstream of the turbine, through which the tank cooling path is connected or can be connected to the exhaust path. By opening the valve, air or exhaust gas is delivered from the exhaust path through the tank cooling path to the tank system for cooling. In the two-position three-way valve embodiment, the attachment from the tank cooling path to the exhaust path can be achieved with only one valve, thus being particularly simple.
[0024] According to another preferred embodiment of the invention, the at least one fuel cell stack is integrated into the cooling loop of a cooling system, which includes a coolant pump for delivering coolant and a main cooler. The cooling system can cool the at least one fuel cell stack, specifically, not only during normal operation, but also before, during, and / or after refueling the storage system, to pre-cool the exhaust gas delivered to the turbine.
[0025] Furthermore, it is proposed that a cooler be integrated into the air supply path downstream of the at least one air compressor. This cooler integrated into the air supply path can cool the air previously compressed by the at least one air compressor, as the air heats up significantly during compression. The cooler is preferably implemented as a heat exchanger through which the coolant in the cooling circuit or exhaust gas flows in the exhaust path. In a least desirable case, the heat exchanger is preferably implemented as a gas-liquid heat exchanger. In the latter case, the heat exchanger is preferably implemented as a gas-gas heat exchanger.
[0026] Advantageously, the supply and exhaust paths are connected or connectable via a bypass path that bypasses the at least one fuel cell stack and integrates a bypass valve. Air from the supply path can be directly introduced into the exhaust path via the bypass path, bypassing the at least one fuel cell stack. This delivers air to the turbine instead of exhausting it. Preferably, this air is pre-compressed by the at least one air compressor and cooled by a cooler integrated downstream of the air compressor in the supply path.
[0027] Preferably, a shut-off valve is integrated into the air supply path to isolate the at least one fuel cell stack from the air supply path. If it is desired to supply only air to the turbine instead of exhaust gas, the shut-off valve can be closed while a bypass valve integrated into the bypass path is opened.
[0028] Cooling of the tank system using air or exhaust gas branching off from the exhaust path can be achieved in several different ways. For example, a heat exchanger can be integrated into the tank system, through which the tank cooling path passes. The deeply cooled air or exhaust gas delivered to the heat exchanger via the tank cooling path absorbs and removes the heat generated during filling.
[0029] Alternatively, at least one temperature-critical component of the tank system is integrated into the tank cooling path, allowing it to directly face the deeply cooled air or exhaust gas in the tank cooling path. In this case, an additional heat exchanger can be eliminated. Attached Figure Description
[0030] Preferred embodiments of the present invention are described below with reference to the accompanying drawings. The drawings show: Figure 1 This is a schematic diagram of the first fuel cell system according to the present invention. Figure 2 This is a schematic diagram of the second fuel cell system according to the present invention. Figure 3 For use in describing in Figure 1 A flowchart illustrating the preferred method for the refueling of the fuel cell system's storage tank system before, during, and / or after refueling, and... Figure 4 For use in describing in Figure 2A flowchart illustrating the preferred method for the fuel cell system's storage tank system before, during, and / or after refueling. Detailed Implementation
[0031] from Figure 1 As can be seen from the fuel cell system 1 according to the present invention, it includes a fuel cell stack 2 having a cathode 2.1 and an anode 2.2. Furthermore, the fuel cell system 1 has an air system 20 for supplying air to the cathode 2.1 of the fuel cell stack 2. The air system 20 includes an air supply path 3, in which a first air compressor 4 driven by an electric motor and a second air compressor 4 driven by a turbine 6 are integrated. Figure 1 As shown, the second air compressor 4 may optionally be equipped with an electric motor as a drive unit. The order of the air compressors 4 can also be interchanged. The air system 20 also includes an exhaust path 5 for discharging exhaust gas from the cathode 2.1.
[0032] Because air heats up significantly during compression, a cooler 14 is integrated into the air supply path 3 downstream of the second air compressor 4. Figure 1 In this configuration, cooler 14 is implemented as a gas-to-gas heat exchanger, through which exhaust gas flows in exhaust path 5. The air in supply path 3 is thus cooled by the exhaust gas in exhaust path 5. This is feasible because fuel cell stack 2 is cooled by cooling system 10, which includes cooling circuit 11, a coolant pump 12 integrated in cooling circuit 11 for delivering coolant, and a main cooler 13 integrated in cooling circuit 11. To ensure that the exhaust gas exiting cathode 2.1 is colder than the air supplied to cathode 2.1, the delivery power of coolant pump 12 can be increased, allowing more coolant to pass through main cooler 13. Simultaneously, bypass path 18 bypassing main cooler 13 is blocked by closing bypass valve 19. In this way, fuel cell stack 2 and the air supplied to cathode 2.1 of fuel cell stack 2 can be cooled to near ambient temperature.
[0033] Downstream of the gas-to-gas heat exchanger, turbine 6 is integrated into exhaust path 5. Exhaust gas is depressurized in turbine 6, where it is significantly cooled. This deeply cooled exhaust gas is not released into the environment under certain conditions, but is branched into tank cooling path 9 by manipulating valve 8 integrated downstream of turbine 6 in exhaust path 5. Tank cooling path 9 connects exhaust path 5 to tank system 7, which stores hydrogen required for the anode 2.2 of fuel cell stack 2. With the deeply cooled exhaust gas input via tank cooling path 9, tank system 7 can be cooled before, during, and / or after refueling. For this purpose, the following combination can be implemented... Figure 3 The steps described: In step S10, the filling of the storage tank system 7 is initiated. In the subsequent step S11, the air compressor 4 is operated to increase the compression ratio. Depending on the cathode-side pressure, the anode-side pressure level and / or the pressure level in the cooling circuit 11 must then be increased in step S12 if necessary, as there is a risk of leaks if the pressure difference is too high. In step S13, the coolant temperature is brought to ambient temperature by closing the bypass valve 19 and / or increasing the delivery power of the coolant pump 12. In step S14, the fuel cell stack 2 is cooled accordingly by the coolant delivered through the fuel cell stack 2 by the coolant pump 12. In an optional step S15, current can be drawn to avoid excessively high individual cell voltages and thus prevent premature degradation of the individual cells in the fuel cell stack 2. The exhaust gas from the fuel cell stack 2 is then delivered to the turbine 6 via a gas-to-gas heat exchanger, and significantly cooled in the turbine 6 by expansion cooling in step S16. Next, in step S17, valve 8 is opened, and the significantly cooled exhaust gas is delivered to the storage tank system 7 through the storage tank cooling path 9 for cooling. In step S18, performed during and / or after refueling, it is checked whether the temperature in the tank system 7 is below a predetermined temperature threshold. If so, cooling of the tank system 7 can be terminated in step S19 by closing valve 8.
[0034] from Figure 2 See another fuel cell system 1 according to the present invention. It is similar to... Figure 1 The difference in the fuel cell system lies primarily in the fact that the cooler 14, integrated downstream of the two air compressors 4 in the air supply path 3, is implemented as a gas-liquid heat exchanger. This heat exchanger is also integrated into the cooling circuit 11, allowing the liquid coolant to flow through it. Furthermore, a bypass path 15 with an integrated bypass valve 16 branches downstream of the cooler 14 to bypass the fuel cell stack 2. The bypass path 15 connects upstream of the turbine 6 to the exhaust path 5. Additionally, two shut-off valves 17 are provided, by which the fuel cell stack 2 is isolated from the air system 20. Figure 2 The fuel cell system 1 shown can also achieve cooling of the storage tank system 7 through expansion cooling before, during, and / or after refueling. For this purpose, instead of exhaust gas that has been depressurized and thus deeply cooled by the turbine 6, the air supplied to the storage tank system 7 is deeply cooled air depressurized by the turbine 6. This method is described below in conjunction with... Figure 4 Describe: In step S20, the filling of the storage tank system 7 is initiated. In the subsequent step S21, the shut-off valve 17 is closed and the bypass valve 16 is opened, thereby isolating the fuel cell stack 2 from the air system 20. Then, in step S22, the two air compressors 4 are operated, increasing the compression ratio. The air, which heats up significantly during compression, is then cooled in step S23 by means of a cooler 14 downstream of the air compressors 4, so that the air temperature preferably corresponds to the ambient temperature. The compressed and cooled air is then passed directly from the supply path 3 to the exhaust path 5 via the bypass path 15, and from there to the turbine 6. In step S24, the air is further significantly cooled by expansion cooling in the turbine 6. In step S25, valve 8 is opened, delivering the significantly cooled air to the storage tank system 7 for cooling via the storage tank cooling path 9. In step S26, performed during and / or after filling, it is checked whether the temperature in the storage tank system 7 is below a predetermined temperature threshold. If so, the cooling of the storage tank system 7 is ended in step S27 by closing valve 8.
Claims
1. Method for operating a fuel cell system (1) comprising at least one fuel cell stack (2) having a cathode (2.1) and an anode (2.2), wherein During normal operation, - Air is supplied to the cathode (2.1) via the air supply path (3), the air being compressed beforehand by at least one air compressor (4) integrated in the air supply path (3), and the exhaust from the cathode (2.1) is supplied via the exhaust path (5) to the turbine (6) integrated in the exhaust path (5) and connected to the air compressor (4). - Hydrogen gas from a storage tank system (7) having at least one compressed gas container is supplied to the anode (2.2). The feature is that the storage tank system (7) is cooled before, during and / or after filling, wherein air or exhaust is used for cooling, which is branched from the exhaust path (5) downstream of the turbine (6) by opening the valve (8) and delivered to the storage tank system (7) via the storage tank cooling path (9).
2. The method of claim 1, wherein, The at least one fuel cell stack (2) is cooled by means of a cooling system (10) which includes a cooling circuit (11) and a main cooler (13), the cooling circuit having a coolant pump (12) for delivering coolant.
3. The method according to claim 1 or 2, characterized in that, The air or exhaust gas used for cooling the storage tank system (7) is compressed in advance by means of the at least one air compressor (4) and cooled by means of a cooler (14) integrated in the air supply path (3) downstream of the at least one air compressor (4), wherein preferably, a heat exchanger integrated in the air supply path (3) is used as the cooler (14), which is passed by the coolant of the cooling system (10) or by the exhaust gas in the exhaust path (5).
4. The method according to any one of the preceding claims, characterized in that, To cool the storage tank system (7), air is used and introduced from the supply path (3) into the exhaust path (5) via a bypass path (15) that bypasses the at least one fuel cell stack (2) and has an integrated bypass valve (16). Open the bypass valve (16) and close the shut-off valve (17) located in the gas supply path (3).
5. The method according to any one of the preceding claims, characterized in that, The tank system (7) and / or at least one temperature-critical component of the tank system (7) directly faces the air or exhaust in the tank cooling path (9).
6. The method according to any one of claims 1 to 4, characterized in that, Air or exhaust in the tank cooling path (9) is guided through a heat exchanger integrated in the tank system (7).
7. A fuel cell system (1), comprising: - At least one fuel cell stack (2) having a cathode (2.1) and an anode (2.2). - An air system (20) for supplying air to the cathode (2.1) of the at least one fuel cell stack (2), wherein the air system (20) has a supply path (3) and an exhaust path (5), the supply path having at least one air compressor (4) integrated in the supply path (3), and the exhaust path having a turbine (6) integrated in the exhaust path (5) and operatively connected to the air compressor (4), and - A tank system having at least one compressed gas container for storing hydrogen (7). The feature is that a storage tank cooling path (9) branches off from the exhaust path (5) downstream of the turbine (6), through which air or exhaust can be delivered to the storage tank system (7) for cooling.
8. The fuel cell system (1) according to claim 7, characterized in that, Downstream of the turbine (6), a valve (8), such as a two-position three-way valve, is integrated into the exhaust path (5), through which the tank cooling path (9) is connected or can be connected to the exhaust path (5).
9. The fuel cell system (1) according to claim 7 or 8, characterized in that, The at least one fuel cell stack (2) is integrated in the cooling loop (11) of a cooling system (10), which includes a coolant pump (12) for delivering coolant and a main cooler (13).
10. The fuel cell system (1) according to any one of claims 7 to 9, characterized in that, Downstream of the at least one air compressor (4), a cooler (14) is integrated in the air supply path (3), which is preferably implemented as a heat exchanger through which the coolant of the cooling circuit (11) or the exhaust gas in the exhaust path (5) flows.
11. The fuel cell system (1) according to any one of claims 7 to 10, characterized in that, The gas supply path (3) and the exhaust path (5) are connected or can be connected via a bypass path (15) that bypasses the at least one fuel cell stack (2), the bypass path being integrated with a bypass valve (16).
12. The fuel cell system (1) according to any one of claims 7 to 11, characterized in that, A shut-off valve (17) for separating the at least one fuel cell stack (2) from the gas supply path (3) is integrated in the gas supply path (3).
13. The fuel cell system (1) according to any one of claims 7 to 12, characterized in that, A heat exchanger is integrated in the storage tank system (7), and the cooling path (9) of the storage tank passes through the heat exchanger.
14. The fuel cell system (1) according to any one of claims 7 to 12, characterized in that, At least one temperature-critical component of the tank system (7) is integrated into the tank cooling path (9).