Fuel cell system and operation method

Abstract

The present invention relates to a fuel cell system (1) comprising an expansion machine (2) for performing mechanical work, having a high-pressure side (3a) and a low-pressure side (3b), and a plurality of fuel cells (4) stacked on top of each other, which are in fluid communication with the high-pressure side of the expansion machine (2) via a gas passage (5). As a result, the exhaust gas containing water discharged from the fuel cells (4) into the gas passage (5) during operation of the fuel cell system (1) drives the expansion machine (2). The fuel cell system (1) further comprises a water separator (6) disposed in the gas passage (5) for separating water from the exhaust gas, and a valve device (7) disposed between the water separator (6) and the high-pressure side (3a) of the expansion machine (2) for adjusting the amount of exhaust gas supplied to the expansion machine (2). Furthermore, the fuel cell system (1) comprises a bypass gas passage (8) through which the exhaust gas can flow, which branches off from the gas passage (5) between the fuel cells (4) and the water separator (6) and is in fluid communication with the low-pressure side (3b) of the expansion machine (2), whereby the exhaust gas can be guided past the expansion machine (2) via the bypass gas passage (8). Furthermore, a bypass valve device (9) for adjusting the amount of exhaust gas flowing through the bypass gas passage (8) is disposed in the bypass gas passage (8).

Description

Technical Field

[0001] The present invention relates to a fuel cell system and a method for operating such a fuel cell system.

[0002] It is known and increasingly important to use fuel cells in motor vehicles. A fuel cell system is typically formed by a plurality of fuel cells stacked on top of each other. Such a stack consisting of fuel cells is often also called a "stack". Individual fuel cells generate water-containing exhaust gas during operation, and this exhaust gas is carried out of the stack by an exhaust gas device. In the exhaust gas line of this exhaust gas device, there is typically an expansion machine that can be driven by the exhaust gas and thus performs mechanical work.

[0003] In order to prevent damage to the expansion machine caused by water contained in the exhaust gas, a water separator is usually arranged upstream of the expansion machine in the exhaust gas line. This water separator must be designed to be able to remove water from the exhaust gas even during cold start of a fuel cell system that generates particularly large amounts of water. However, such a designed water separator generates a relatively high pressure drop in the exhaust gas line both during cold start and normal operation of the fuel cell system, and this pressure drop increases the consumption of the fuel cell system and thus reduces the efficiency of the fuel cell system.

[0004] Therefore, an object of the present invention is to provide an improved embodiment of a fuel cell system that addresses the aforementioned problems.

[0005] This object is solved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0006] Accordingly, the basic idea of the present invention is to provide a bypass in the exhaust gas device of a fuel cell system that can guide the exhaust gas beside the expansion machine, particularly during the cold start of the fuel cell system described at the beginning, so that there is no risk of damage to the expansion machine caused by the water present in the exhaust gas. In this case, the bypass branches off from the exhaust gas system not only upstream of the expansion machine but also upstream of the water separator. Therefore, the water separator can be designed with a correspondingly lower output because the water separator only needs to separate water from the exhaust gas during normal operation and does not need to separate it during cold start. Nevertheless, such a design of the water separator advantageously results in less pressure loss, thereby also improving the efficiency of the fuel cell system.

[0007] To control the bypass and thus the amount of exhaust gas guided beside the expansion machine, one valve is provided in each of the original exhaust gas system and the bypass. By means of this valve, it is possible to adjust what proportion of the exhaust gas should be supplied to the expansion machine and what proportion should be guided beside the expansion machine by the bypass. This ratio may be adapted to the individual operating conditions during the operation of the fuel cell system. This is particularly applicable to the cold start of a fuel cell system that enables the exhaust gas to be temporarily and completely guided beside the expansion machine through the bypass by closing the valve assigned to the expansion machine.

[0008] The valve device and the bypass valve device may be configured as in the prior art, which means that both valve devices have a valve opening surrounded by a valve seat provided in the gas passage or the bypass gas passage. Further, the valve device or the bypass valve device includes a displaceable valve body that contacts the valve seat in the closed position and fluid-tightly closes the valve opening, thereby preventing the exhaust gas from flowing through the valve opening. In contrast, in the open position different from the closed position, the valve opening is open for the flow of the exhaust gas. Further, the valve device or the bypass valve device may be designed to be able to displace the valve body to an intermediate position between the open position and the closed position. In this case, in particular, the open cross-section of the valve opening that is open for the flow of the exhaust gas may be increased by the movement of the valve body from the closed position to the open position. Thus, the opening degree of the valve device or the bypass valve device can be changed.

[0009] Specifically, the fuel cell system according to the present invention includes an expansion machine for performing mechanical work, which has a high-pressure side and a low-pressure side. Further, the fuel cell system includes a plurality of, that is, at least two fuel cells stacked on top of each other. These fuel cells are in fluid communication with the high-pressure side of the expansion machine via a gas passage, whereby the exhaust gas discharged from the fuel cell into the gas passage during the operation of the fuel cell system and containing water at the time of discharge drives the expansion machine. The gas passage may be part of an exhaust gas device or an exhaust gas system of the fuel cell system.

[0010] Furthermore, the fuel cell system includes a water separator disposed in the gas passage for separating water from the exhaust gas. A valve device of the fuel cell system for adjusting the amount of exhaust gas supplied to the expansion machine is disposed between the water separator and the high-pressure side of the expansion machine.

[0011] According to the present invention, the fuel cell system further includes a bypass gas passage through which exhaust gas can flow. This bypass gas passage branches off from the gas passage between the fuel cell and the water separator, whereby the exhaust gas can be guided past the expander via the bypass gas passage. The bypass gas passage may rejoin the gas passage downstream of the expander. A bypass valve device of the fuel cell system for adjusting the amount of exhaust gas flowing through this bypass gas passage is disposed in the bypass gas passage.

[0012] Advantageously, the expander may be a gas turbine. Preferably, this expander or gas turbine includes a rotatable turbine wheel that can be driven by the exhaust gas.

[0013] Particularly preferably, the valve device disposed in the gas passage may be a pressure regulating valve for performing closed-loop control of the gas pressure of the exhaust gas, or may include a pressure regulating valve. In particular, this pressure regulating valve may be configured such that the pressure at the cathode of the fuel cell is closed-loop controlled to a specified target value by appropriately adjusting this pressure regulating valve.

[0014] Also particularly preferably, the bypass valve device disposed in the bypass gas passage may also be a pressure regulating valve, or may include a pressure regulating valve. This pressure regulating valve may also be configured such that the pressure at the cathode of the fuel cell is closed-loop controlled to a specified target value by appropriately adjusting this pressure regulating valve.

[0015] Particularly advantageously, the valve device and the bypass valve device may be formed as the same member with respect to each other. By this characteristic, the structure of the fuel cell system is simplified, and thus, cost merits during the production of the fuel cell system can be obtained.

[0016] According to an advantageous refinement, the fuel cell system comprises an open-loop control / closed-loop control device which can adjust the valve device and the bypass valve device, respectively, between an open position in which the exhaust gas can flow through the valve device and a closed position in which the flow through by the exhaust gas is blocked. By means of the open-loop control / closed-loop control device configured in this way, the positions of the valve devices can be adapted to different operating situations. Thereby, it is possible to determine what proportion of the exhaust gas arriving from the fuel cell should be supplied to the expansion machine and what proportion should be guided past the expansion machine. In particular, it becomes possible to operate the fuel cell system in different operating states. In particular, it is thus possible to take into account that when the fuel cell is cold-started, the exhaust gas contains particularly a lot of water, and thus this water can be guided past the expansion machine via a bypass in order to protect the expansion machine.

[0017] In a further preferred embodiment, the fuel cell system according to the invention is switchable between a nominal operating state and a cold-start operating state by means of an open-loop control / closed-loop control device. In this embodiment, in the nominal operating state, the valve device is not adjusted to the closed position. That is to say, the valve device is adjusted to the open position or to an intermediate position between the closed position and the open position. In any case, a defined amount of exhaust gas thus reaches the expansion machine and can drive this expansion machine. In this case, since the water separator can separate the water contained in the exhaust gas, this water no longer reaches the expansion machine. In the cold-start operating state, the bypass valve device is not adjusted to the closed position. Thus, at least a part of the exhaust gas is guided past the expansion machine. In this way, an overload on the water separator due to an increase in the amount of water in the exhaust gas is prevented.

[0018] According to an advantageous refinement, in the cold-start operating state, the valve device is adjusted to the closed position. In this way, the expansion machine is protected as well as possible against damage by water during cold start.

[0019] According to a further advantageous improvement, in the nominal operating state, the bypass valve device is adjusted to the closed position. Thereby, all the exhaust gases are supplied to the expander machine, and thus the efficiency of the fuel cell system is maximized.

[0020] Since the present invention further relates to a motor vehicle comprising the fuel cell system according to the present invention described above, the advantages of the fuel cell system according to the present invention are transferred to the motor vehicle according to the present invention.

[0021] Since the present invention further relates to a method for operating the above-described fuel cell system provided with an open-loop control / closed-loop control device, the advantages of the fuel cell system according to the present invention are also transferred to the method according to the present invention. According to this method, after the start of operation of the fuel cell system, that is, after activation, first, it is switched to the cold start operating state, operated in this cold start operating state, and then switched from the cold start operating state to the nominal operating state at a later time point.

[0022] Further important features and advantages of the present invention will become apparent from the dependent claims, the drawings and the corresponding description of the drawings based on the drawings.

[0023] Of course, the features described above and the features further described below can be used not only in the combinations described respectively, but also in other combinations or alone without departing from the scope of the present invention.

[0024] Preferred embodiments of the present invention are shown in the drawings and will be described in detail in the following description. Note that the same reference numerals correspond to the same or similar components or components that are functionally the same.

Brief Description of the Drawings

[0025]

Figure 1

[0026] Only in Figure 1, an example of the fuel cell system 1 according to the present invention is shown schematically. This fuel cell system 1 includes an expansion machine 2 for performing mechanical work, which has a high-pressure side 3a and a low-pressure side 3b. In an exemplary scenario, this expansion machine 2 is a gas turbine 10. The expansion machine 2 or the gas turbine 10 may include a rotatable and exhaust gas drivable turbine wheel (not shown, indicated by the dashed line 12 in Figure 1) that divides the expansion machine 2 or the gas turbine 10 into a high-pressure side 3a and a low-pressure side 3b.

[0027] The fuel cell system 1 further includes a plurality of fuel cells 4 stacked on top of each other, and these fuel cells 4 are in fluid communication with the high-pressure side 3a of the expansion machine 2 via a gas path 5. Therefore, the exhaust gas discharged from the fuel cells 4 into the gas path 5 during the operation of the fuel cell system 1 can drive the expansion machine 2. Water is contained in the exhaust gas. Therefore, a water separator 6 for separating water from the exhaust gas is provided in the gas path 5 before the exhaust gas reaches the expansion machine 2. Further, the fuel cell system 1 includes a bypass gas path 8 through which the exhaust gas can flow. This bypass gas path 8 branches from the gas path 5 at a branch point 13 between the fuel cell 4 and the water separator 6, is guided beside the expansion machine 2, and rejoins the gas path 5 at a confluence point 14 on the downstream side of the expansion machine 2. That is, the exhaust gas can be guided beside the expansion machine 2 via the bypass gas path 8. In the gas path 5, a valve device 7 for adjusting the amount of exhaust gas supplied to the expansion machine 2 is arranged between the water separator 6 and the high-pressure side 3a of the expansion machine 2. Similarly, in the bypass gas path 8, a bypass valve device 9 for adjusting the amount of exhaust gas flowing through this bypass gas path 8 and thus guided beside the expansion machine 2 is arranged.

[0028] The valve device 7 arranged in the gas path 5 is formed by a pressure regulating valve. Also, the bypass valve device 9 arranged in the bypass gas path 8 may also be formed by a pressure regulating valve. The valve device 7 and the bypass valve device 9 or both pressure regulating valves may be formed as the same member with each other.

[0029] The fuel cell system 1 further includes an open-loop control / closed-loop control device 11. By this open-loop control / closed-loop control device 11, both the valve device 7 disposed in the gas passage 5 and the bypass valve device 9 disposed in the bypass gas passage 8 can be adjusted between an open position and a closed position. In the open position, the exhaust gas can flow through the valve device 7 or the bypass valve device 9. In contrast, in the closed position, the flow of the exhaust gas to the valve device 7 or the bypass valve device 9 is blocked. The valve device 7 and the bypass valve device 9 can also be adjusted to intermediate positions between the open position and the closed position, respectively.

[0030] The fuel cell system 1 may be switched between a nominal operating state and a cold start operating state by the open-loop control / closed-loop control device 11. The valve device 7 is adjusted to the closed position in the cold start operating state and is adjusted to a position different from the closed position in the nominal operating state. This position different from the closed position may be the open position. The bypass valve device 9 is adjusted to the closed position in the nominal operating state and is adjusted to a position different from the closed position in the cold start operating state. This position different from the closed position may be the open position.

[0031] In the fuel cell system 1 exemplarily described above, the method according to the present invention may be implemented. According to this method, after the operation start of the fuel cell system 1, that is, after activation, first, it is switched to the cold start operating state, operated in this cold start operating state, and later switched from the cold start operating state to the nominal operating state.

Claims

1. A fuel cell system for automobiles (1), An expansion machine (2) for performing mechanical work, having a high-pressure side (3a) and a low-pressure side (3b), Multiple fuel cells (4) are stacked on top of each other, and are in fluid communication with the high-pressure side of the expansion machine (2) via a gas passage (5), thereby allowing exhaust gas containing water, discharged from the fuel cells (4) into the gas passage (5) during the operation of the fuel cell system (1), to drive the expansion machine (2). A water separator (6) for separating water from the exhaust gas is located within the gas passage (5), A valve device (7) for adjusting the amount of exhaust gas supplied to the expansion machine (2) is positioned between the water separator (6) and the high-pressure side (3a) of the expansion machine (2), A bypass gas passage (8) is provided between the fuel cell (4) and the water separator (6), branching off from the gas passage (5), which can guide the exhaust gas alongside the expansion machine (2), and through which the exhaust gas can pass. A bypass valve device (9) is located within the bypass gas passage (8) to adjust the amount of exhaust gas flowing through the bypass gas passage (8). A fuel cell system (1) comprising:

2. The fuel cell system according to claim 1, characterized in that the expansion machine (2) is a gas turbine (10).

3. The fuel cell system according to claim 1 or 2, characterized in that the valve device (7) located in the gas passage (5) is a pressure regulating valve, or comprises a pressure regulating valve.

4. The fuel cell system according to claim 1 or 2, characterized in that the bypass valve device (9) located in the bypass gas passage (8) is a pressure regulating valve, or comprises a pressure regulating valve.

5. The fuel cell system according to claim 1 or 2, characterized in that the valve device (7) and the bypass valve device (9) are formed as the same component.

6. The fuel cell system (1) is characterized by comprising an open-loop control / closed-loop control device (11) that can adjust the valve device (7) and the bypass valve device (9) between an open position in which the exhaust gas can flow through the valve device and a closed position in which the flow of the exhaust gas is blocked, respectively, as described in claim 1 or 2.

7. The fuel cell system (1) is switchable between a nominal operating state and a cold start operating state by the open-loop control / closed-loop control device (11). In the nominal operating state, the valve device (7) is not adjusted to the closed position, and in the cold start operating state, the bypass valve device (9) is not adjusted to the closed position. A fuel cell system according to claim 6, characterized in that...

8. The fuel cell system according to claim 7, characterized in that, in the cold start operation state, the valve device (7) is adjusted to the closed position.

9. The fuel cell system according to claim 7, characterized in that, in the cold start operation state, the bypass valve device (9) is not adjusted to the closed position.

10. The fuel cell system according to claim 7, characterized in that, in the nominal operating state, the bypass valve device (9) is adjusted to the closed position.

11. An automobile comprising the fuel cell system according to claim 1 or 2.

12. A method for operating the fuel cell system described in claim 7, The fuel cell system is switched to the cold start operating state after it has started operating, and then switched from the cold start operating state to the nominal operating state at a later point. method.

Images