Charged fuel cell system with enrichment device

Abstract

The invention relates to a fuel cell system (100) comprising a fuel cell stack (1), a cathode path (2) for supplying the fuel cell stack (1) with a first reaction gas containing an oxidizing agent, an anode path (3) for supplying the fuel cell stack (1) with a second reaction gas containing a fuel gas, and a control unit for controlling the system (100), wherein the cathode path (2) comprises a first gas supply line (21) and a first exhaust line (22), and the anode path (3) comprises a second gas supply line (31) and a second exhaust line (32), wherein at least one charge air cooler (6), a humidifier (7), a first compressor-turbine unit (4), and an enrichment device (2a) are arranged in the cathode path (2), wherein the enrichment device (2a) is connected to the first gas supply line (21) and comprises a second compressor-turbine unit (5).

Description

[0001] The invention relates to a fuel cell system with an enrichment device, in particular an oxygen enrichment device, a method for operating the fuel cell system and a vehicle comprising the fuel cell system.

[0002] From DE 10 2016 009 932 A1 a fuel cell system is known which comprises an oxygen enrichment device, wherein inert gas flowing out of the oxygen enrichment device is used to operate a gas storage of a compressor.

[0003] The device according to the invention comprises a fuel cell system which comprises a fuel cell stack, a cathode path for supplying the fuel cell stack with a first reaction gas containing an oxidizing agent, an anode path for supplying the fuel cell stack with a second reaction gas containing a fuel gas, and a control unit for controlling the system, wherein the cathode path comprises a first gas supply line and a first exhaust gas line, and the anode path comprises a second gas supply line and a second exhaust gas line, wherein at least one charge air cooler, a humidifier, a first compressor-turbine unit, and an enrichment device are arranged in the cathode path, wherein the enrichment device is connected to the first gas supply line and comprises a second compressor-turbine unit.

[0004] The fuel cell stack comprises a plurality of individual cells, each with a cathode supplied with the first reaction gas, for example, air, and an anode supplied with a fuel gas, for example, hydrogen. Membranes permeable to charge carriers between the anodes and cathodes allow charge carrier transport between the gases and thus the tapping of a voltage between the anode and cathode. The fuel cells can, in particular, be polymer electrolyte fuel cells.

[0005] The humidifier of the fuel cell system, for example, is arranged so that both the first gas supply line and the first exhaust line pass through it, thus utilizing water-containing cathode exhaust gas to humidify the dry first reaction gas. The compressor-turbine units each comprise a compressor and a turbine, each of which is rotationally fixed to a shaft, which can be driven, for example, by an electric motor. The compressors serve to compress the unused first reaction gas, while the turbines utilize the energy of an exhaust gas flow to increase the boost pressure.

[0006] The enrichment device serves to enrich the first reaction gas with an oxidizing agent or an inert gas. It can also be used to enrich the second reaction gas with an inert gas.

[0007] The fuel cell system according to the invention allows the enrichment of the first reaction gas with an oxidizing agent, e.g., oxygen, or an inert gas, e.g., nitrogen. This can, on the one hand, increase the efficiency and power density of the fuel cell stack, and, on the other hand, allows for advantageous and efficient operating strategies, which are described below. In particular, the use of two compressors and their clever arrangement within the cathode path allows for the effective use of membrane separators to enrich the first reaction gas.

[0008] Preferably, the enrichment device comprises a membrane separator and further comprises a first and a second supply line through which the enrichment device is supplied with the first reaction gas and comprises a first and a second coupling line which couple the enrichment device to the first gas supply line, wherein the first and second supply lines and coupling lines are connected to the membrane separator and the membrane separator has a selectively permeable membrane through which the first reaction gas can be enriched with oxidant in the first coupling line and with inert gas in the second coupling line.

[0009] The selectively permeable membrane of the membrane separator allows higher amounts of oxidizing agent to pass through the membrane than inert gas components.

[0010] Preferably, a first flow path of the first reaction gas leads from the first feed line into the membrane separator and further into the first coupling line and a second flow path of the first reaction gas leads from the second feed line into the membrane separator and further into the second coupling line, wherein a compressor of the compressor-turbine unit is arranged in the second feed line and the enrichment device comprises a third exhaust gas line which branches off from the second coupling line and the turbine of the second compressor-turbine unit is arranged in the third exhaust gas line.

[0011] Such an arrangement enables a countercurrent arrangement of the membrane, with the first reaction gas flowing from different sides. The use of a compressor in one of the feed lines results in a pressure difference on the opposite sides of the membrane, which increases the permeation rate of the oxidant and thus leads to more effective enrichment.

[0012] Preferably, the first coupling line merges into the first gas supply line upstream of the compressor of the first compressor-turbine unit, and the second coupling line opens into the first gas supply line at a connection downstream of the compressor. The second coupling line preferably comprises a three-way valve upstream of the connection, with a system bypass coupled to the three-way valve, which connects the second coupling line to the first exhaust line.

[0013] This arrangement allows the targeted feeding of charged reaction gas enriched with oxidant or inert gas into the first gas supply line. Using the three-way valve, a flow path can be created from the second coupling line directly into the first exhaust line, from the second coupling line into the first gas supply line, or from the first exhaust line into the first gas supply line. This allows, on the one hand, the efficiency of the fuel cell system to be increased compared to systems without enrichment, and, on the other hand, operating strategies of the fuel cell system, such as effective cathode gas recirculation or inerting of the stack during system shutdown, to be enabled.

[0014] Preferably, a third coupling line is connected to the system bypass, which coupling the second coupling line to the second gas supply line, wherein a third shut-off valve is arranged in the third coupling line.

[0015] Using the third coupling line, the anode gas can be enriched with inert gas, which leads to a beneficial mitigation of degradation effects of the fuel cells during so-called air-to-air starts of the system and thus to a longer-lasting system.

[0016] Preferably, a first and a second bypass are arranged in the first exhaust line, wherein the exhaust gas flowing from the fuel cell stack can be guided around the humidifier with the first bypass and the exhaust gas can be guided around the turbine of the first compressor-turbine unit with the second bypass, wherein a first shut-off valve is arranged in the first bypass and a second shut-off valve is arranged in the second bypass.

[0017] The first and second bypasses provide additional options for controlling the moisture content and pressure within the fuel cell stack. Alternatively or additionally, the water content and pressure within the stack can be controlled by controlling the electric motors of the compressor-turbine units and recirculating the cathode exhaust gas.

[0018] A method according to the invention is designed and configured to operate a fuel cell system according to the invention using the control unit, wherein the fuel cell system preferably further comprises sensors for detecting the load, the output voltage, the moisture content and the pressure in the fuel cell stack, and wherein the method comprises the following steps: a) Detecting the load, output voltage, moisture content and pressure in the fuel cell stack using sensors and transmitting the measured values ​​to the control unit. b) Controlling the three-way valve and / or the first and / or the second and / or the third shut-off valve of the fuel cell system taking into account the measured values ​​or the operating state of the system.

[0019] The sensor system comprises a number of sensors, e.g., those for measuring the electrical current tapped from the stack or the cell voltages, or pressure and humidity sensors arranged at suitable locations in the cathode or anode path. The operating state of the system can be, for example, a shutdown process or an air-to-air start.

[0020] Preferably, the second shut-off valve is controlled by the control unit to regulate the pressure within the fuel cell stack.

[0021] Furthermore, the three-way valve and / or the second and / or the third shut-off valve are preferably controlled by the control unit taking into account the operating state of the fuel cell system or the load and the output voltage of the fuel cell stack, and the three-way valve and / or the first shut-off valve are controlled taking into account the moisture content of the fuel cell stack.

[0022] A vehicle according to the invention is equipped with a fuel cell system according to the invention.

[0023] Preferred embodiments are explained in more detail with reference to the following figure. Fig. 1 a first embodiment of the fuel cell system according to the invention and Fig. 2 a second embodiment of the fuel cell system according to the invention.

[0024] Fig. 1 shows a preferred embodiment of the fuel cell system 100 according to the invention. The fuel cell system 100 comprises a cathode path 2 and an anode path 3, wherein the anode path 3 has a second gas supply line 31 and a second exhaust line 32. The fuel cell stack 1 of the system 100 is supplied with hydrogen from a pressure tank 8 via the anode path 3. Anode exhaust gas is fed from the second exhaust line 32 into the second gas supply line 31 by means of a recirculation line 33 having a recirculation blower 9, or, when the hydrogen concentration is sufficiently low, is expelled from the anode path 3 by opening a discharge valve 44.

[0025] Air is fed into the fuel cell stack 1 via the first gas supply line 21 of the cathode path 2, with used, nitrogen-rich air being expelled via the first exhaust line 22. In the first gas supply line 21, in the air flow direction, there is first the compressor 4a of the first compressor-turbine unit 4, then a charge air cooler 6, and finally a humidifier 7. Located in the flow path of the cathode exhaust gas flow in the first exhaust line 22 are the humidifier 7 and the turbine 4b of the first compressor-turbine unit 4, with the humidifier 7 being able to be bypassed by a first bypass 28 with a first shut-off valve 41, and the turbine 4b being able to be bypassed by a second bypass 29 with a second shut-off valve 42.

[0026] The system 100 further comprises an enrichment device 2a, wherein the device 2a comprises a membrane separator 10 with a selectively permeable membrane 10a. The selectively permeable membrane 10a allows a higher permeation rate for oxygen compared to the other air components. The membrane separator 10 is supplied with air through a first supply line 24a and a second supply line 25a, wherein the two air streams are directed toward opposite sides of the selectively permeable membrane 10a, and the compressor 5a of the second compressor-turbine unit 5 is arranged in the second supply line 25a. The membrane separator 10 is connected to the first gas supply line 21 via a first coupling line 24b and a second coupling line 25b, wherein the second coupling line 25b opens into the first gas supply line 21 at a connection 30 and the first coupling line 24b merges directly into the first gas supply line 21.The first coupling line 24b merges into the first gas supply line 21 upstream of the compressor 4a of the first compressor-turbine unit 4, and the connection 30 of the second coupling line 25b to the first gas supply line 21 is located between the charge air cooler 6 and the humidifier 7. A third exhaust line 23 branches off from the second coupling line 25b. The turbine 5b of the second compressor-turbine unit 5 is arranged in the third exhaust line 23.

[0027] With this arrangement, a first flow path of the air introduced into the system leads through the enrichment device 2a from the first supply line 24a, through the membrane separator 10, and further into the compressor 4a. A second flow path leads from the second supply line 25a into the second coupling line 25b. The compressor 5a of the second compressor-turbine unit 5 generates a pressure in the range of 3-5 bar, here approximately 4 bar, in the second coupling line 25b, while the pressure in the first coupling line 24a is 1 bar. Due to the pressure gradient from one side of the selectively permeable membrane 10a to the other, a transfer of oxygen is induced, so that oxygen-rich air is present in the first coupling line 24b and nitrogen-rich air is present in the second coupling line 25b and the third exhaust line 23. The oxygen-rich air is compressed by the compressor 4a.

[0028] The oxygen or nitrogen concentration of the compressed air fed into the fuel cell stack 1 is regulated by means of a three-way valve 40, which is arranged upstream of the connection 30 of the second coupling line 25b to the first gas supply line 21. In addition, a system bypass 27 is arranged on the three-way valve 40, which connects the second coupling line 25b to the first exhaust line 22. The three-way valve 40 can be switched such that the second coupling line 25b is fluidically connected either to the first gas supply line 21 or to the first exhaust line 22, or the first exhaust line 22 is connected to the first gas supply line 21. A third coupling line 26b with a third shut-off valve 43 located therein in turn connects the second coupling line 25b to the second gas supply line 31. Through this Fig. The arrangement shown in Figure 1 allows the cathode of the fuel cell stack 1 to be supplied with oxygen-rich and nitrogen-rich air. In addition, nitrogen-rich air can be fed into the anode.

[0029] A control unit (not shown) controls the opening degrees and opening paths of all valves of the system 100 as well as the speed of the electrical machines 4c,5c which drive the compressor-turbine units 4,5.

[0030] The Fig. The fuel cell system shown in Figure 1 is operated using an embodiment of the method according to the invention described below: For this purpose, the system 100 has a sensor system (not shown) that includes sensors for measuring the electrical current tapped at the stack 1 and the individual cell voltages. Furthermore, a pressure sensor and a relative humidity sensor, which are arranged between the humidifier 7 and the stack 1 in the first gas supply line 21, are part of the sensor system. In alternative embodiments, the pressure and humidity sensors can be arranged at other suitable locations in the cathode path 2 or anode path 3, and the sensor system can include further suitable sensors.

[0031] All sensors are connected to the control unit of the system 100 and continuously supply it with measurement data on the basis of which the system 100 is operated and the operating state of the system 100 is recorded.

[0032] During full-load operation of the system 100, the performance is advantageously increased by a corresponding enrichment of the cathode with oxygen, since the second coupling line 25b is connected directly to the first exhaust line 22 and the cathode is supplied exclusively with oxygen-rich air.

[0033] During partial load or idle operation of the fuel cell system 100, the cathode is supplied with nitrogen-rich air by appropriately switching the three-way valve 40 (connecting the second coupling line 25b to the first gas supply line 21). Alternatively, the nitrogen-rich air can be provided from the cathode exhaust gas by connecting the first exhaust line 22 to the first gas supply line 21. In this position of the three-way valve 40, the cathode supply air is simultaneously more humidified. By supplying the cathode with nitrogen-rich air, excessively high cell voltages can advantageously be prevented, thus preventing degradation of the stack 1. Flooding of the stack 1 is counteracted, for example, by regulating the degree of opening of the first bypass valve 41, thus reducing the water loading of the gas flowing into the cathode.Alternatively, flooding of the stack 1 can be prevented by switching the three-way valve 40 in such a way that nitrogen-rich air is alternately taken from the enrichment device 2a or the cathode exhaust gas.

[0034] When the system 100 is switched off, the cathode is also supplied with nitrogen-rich air from the enrichment device 2a for inerting purposes, or the cathode exhaust gas is recirculated.

[0035] In the case of so-called air-to-air starts of the fuel cell system 100, in which oxygen is present at the cathode and anode, degradation effects of the stack 1 are reduced by enriching the anode gas with nitrogen.

[0036] Fig. 2 shows a particularly preferred second embodiment of the fuel cell system 100 according to the invention. This embodiment differs from the first embodiment ( Fig. 1). The lines are routed and arranged in such a way that the flow to the opposite sides of the selectively permeable membrane 10a occurs from exactly opposite directions. This particularly promotes the transfer of oxygen from the high-pressure side to the low-pressure side of the membrane. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 009 932 A1

[0002]

Claims

[1] A fuel cell system (100) comprising a fuel cell stack (1), a cathode path (2) for supplying the fuel cell stack (1) with a first reaction gas containing an oxidizing agent, an anode path (3) for supplying the fuel cell stack (1) with a second reaction gas containing a fuel gas, and a control unit for controlling the system (100), wherein the cathode path (2) comprises a first gas supply line (21) and a first exhaust gas line (22), and the anode path (3) comprises a second gas supply line (31) and a second exhaust gas line (32), wherein at least one charge air cooler (6), a humidifier (7), a first compressor-turbine unit (4), and an enrichment device (2a) are arranged in the cathode path (2), wherein the enrichment device (2a) is connected to the first gas supply line (21) and comprises a second compressor-turbine unit (5). [2] Fuel cell system (100) according to claim 1, wherein the enrichment device (2a) comprises a membrane separator (10) and further comprises a first (24a) and a second supply line (25a) through which the enrichment device (2a) is supplied with the first reaction gas and a first (24b) and a second coupling line (25b) which couple the enrichment device (2a) to the first gas supply line (21), wherein the first and second supply lines (24a, 25a) and coupling lines (24b, 25b) are connected to the membrane separator (10) and the membrane separator (10) has a selectively permeable membrane (10a) through which the first reaction gas can be enriched with oxidant in the first coupling line (24b) and with inert gas in the second coupling line (25b). [3] Fuel cell system (100) according to claim 2, wherein a first flow path of the first reaction gas leads from the first supply line (24a) into the membrane separator (10) and further into the first coupling line (24b) and a second flow path of the first reaction gas leads from the second supply line (25a) into the membrane separator (10) and further into the second coupling line (25b), wherein a compressor (5a) of the second compressor-turbine unit (5) is arranged in the second supply line (25a) and the enrichment device (2a) comprises a third exhaust gas line (23) which branches off from the second coupling line (25b) and the turbine (5b) of the second compressor-turbine unit (5) is arranged in the third exhaust gas line (23). [4] Fuel cell system (100) according to one of the preceding claims, wherein the first coupling line (24b) merges into the first gas supply line (21) upstream of the compressor (4a) of the first compressor-turbine unit (4) and the second coupling line (25b) opens into the first gas supply line (21) downstream of the compressor (4a) at a connection (30), and the second coupling line (25b) comprises a three-way valve (40) upstream of the connection (30), wherein a system bypass (27) is coupled to the three-way valve (40), which connects the second coupling line (25b) to the first exhaust gas line (22). [5] Fuel cell system (100) according to one of the preceding claims, wherein a third coupling line (26b) is connected to the system bypass (27), which coupling line couples the second coupling line (25b) to the second gas supply line (31), wherein a third shut-off valve (43) is arranged in the third coupling line (26b). [6] Fuel cell system (100) according to one of the preceding claims, wherein a first (28) and a second bypass (29) are arranged in the first exhaust line (22), wherein the exhaust gas flowing from the fuel cell stack (1) can be guided around the humidifier (7) with the first bypass (28) and the exhaust gas can be guided around the turbine (4b) of the first compressor-turbine unit (4) with the second bypass (29), wherein a first (41) shut-off valve (42) is arranged in the first bypass (28) and a second shut-off valve (42) is arranged in the second bypass (29). [7] A method for operating a fuel cell system (100) according to any one of the preceding claims, wherein the fuel cell system (100) further comprises sensors for detecting the load, the output voltage, the moisture content and the pressure in the fuel cell stack (1), and wherein the method comprises the following steps: c) Detecting the load, the output voltage, the moisture content and the pressure in the fuel cell stack (1) by means of the sensors and transmitting the measured values ​​to the control unit. d) controlling the three-way valve (40) and / or the first (41) and / or the second (42) and / or the third shut-off valve (43) of the fuel cell system (100) taking into account the measured values ​​or the operating state of the system (100). [8] A method for operating a fuel cell system (100) according to claim 7, wherein the second shut-off valve (42) is controlled by the control unit to regulate the pressure within the fuel cell stack (1). [9] Method for operating a fuel cell system (100) according to one of claims 7 or 8, wherein the three-way valve (40) and / or the second (42) and / or the third shut-off valve (43) are controlled by the control unit taking into account the operating state of the fuel cell system (100) or the load and the output voltage of the fuel cell stack (1), and the three-way valve (40) and / or the first shut-off valve (41) are controlled taking into account the moisture content of the fuel cell stack (1). [10] A vehicle comprising a fuel cell system (100) according to any one of claims 1-6.

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