Method for controlling a fuel cell module comprising at least two fuel cell units, and fuel cell module

Abstract

The invention relates to a method (100) for controlling a fuel cell module (10) comprising at least two fuel cell units (11), wherein each fuel cell unit (11) comprises an air inlet (13a) and an air outlet (13b). The method (100) involves measuring (101), for each fuel cell unit, a temperature of the air in an air-side discharge line (70b) downstream of the air outlet (13b) of each fuel cell unit (11) by means of a temperature sensor (40) associated with the fuel cell unit, and controlling (102) the fuel cell module (10) according to the measured temperatures.

Description

[0001] R.416988

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for controlling a fuel cell module comprising at least two fuel cell units and a fuel cell module

[0006] The present invention relates to a method for controlling a fuel cell module and a fuel cell module according to the independent claims.

[0007] State of the art

[0008] Fuel cells are electrochemical energy converters that directly convert chemical energy into electrical energy. They are a promising technology for a wide range of applications, from portable electrical devices to stationary power control systems. A special type of fuel cell is the solid oxide fuel cell (SOFC), which operates at high temperatures and exhibits high efficiency. Electrochemical reactions take place at the interface between an anode and a cathode, separated by an electrolyte. In the prior art, it is known to connect fuel cells in series to form fuel cell units, or fuel cell stacks. Such fuel cell units can then be connected to form fuel cell modules, and modules can be combined to form fuel cell systems.

[0009] Disclosure of the invention

[0010] The present invention is based on the objective of providing an improved control method for a fuel cell module that enables possible independent air-side fluidic control.

[0011] The aforementioned problem is solved by a method for controlling a fuel cell module comprising at least two fuel cell units. Each fuel cell unit preferably comprises several fuel cells connected in series, wherein the fuel cells are in particular R.416988

[0012] - 2 -

[0013] These are solid oxide fuel cells (SOFCs). Each fuel cell unit comprises an anode and a cathode, separated by an electrolyte.

[0014] The fuel cell unit comprises an air inlet and an air outlet for air supplied to and discharged from the cathode. It may also include a gas inlet and a gas outlet for fuel gas, which is preferably supplied to and discharged from the anode. In particular, the fuel cell module comprises a fuel gas supply line up to the gas inlet, a fuel gas discharge line from the gas outlet, and preferably an air supply line up to the air inlet and an air discharge line from the air outlet.

[0015] Both the fuel gas and air supply lines can follow a fuel cell module-specific path up to a junction point where the supply line branches off to the individual fuel cell units, thus dividing the flow rate. From the junction point onward, the supply line can therefore transition into individual paths specifically assigned to the fuel cell units, while upstream of the junction, a path is provided that serves the entire fuel cell module. The same applies to the downstream lines. Here, too, a downstream line can initially comprise individual paths for each fuel cell unit, while these converge from a junction point onward.

[0016] The method involves measuring the air temperature in an air-side duct downstream of the air outlet of each fuel cell unit using a temperature sensor assigned to that unit. These sensors are primarily located in the paths specifically assigned to the fuel cell units. In other words, a temperature sensor is provided in the specific air-side duct of each fuel cell unit, allowing the temperature of each unit to be measured and the fuel cell module to be controlled accordingly.

[0017] At least one temperature sensor can also be arranged in the path of the derivation that is assigned to the fuel module, i.e., behind a node from which the airflows of the derivations of the individual R.416988

[0018] - 3 -

[0019] The fuel cell paths of the derivation are combined. These thus measure the average temperature of the air streams.

[0020] Depending on the temperature, the air flow rate in the air-side supply line can be controlled. The air flow rate can be controlled in the supply line path assigned to at least one fuel cell unit and / or in a supply line path assigned to the fuel cell module. In other words, the flow rate in the respective air-side supply line to individual fuel cell units can be adjusted so that the change in flow rate affects only one or more fuel cell units. Furthermore, the change can affect the air flow rate for the entire fuel cell module. Specifically, the flow rate can be controlled in a path assigned to a fuel cell unit and / or in the common supply line path before the volume flows are divided among the different fuel cell units.

[0021] The supply line can include a feed unit and at least one valve, preferably located at the beginning of the air-side supply line. The flow rate can be influenced by controlling the at least one valve and / or the feed unit. The feed unit can be designed as a blower that delivers the quantity of air supplied to the supply line. Provided that the air is supplied at sufficient pressure at the beginning of the supply line, only one valve can be provided at this point.

[0022] For example, the airflow rate supplied to the entire module can be influenced by a feed unit located at the beginning of the air supply line. Increasing the total volume moved by the feed unit increases the corresponding flow rate. This can be determined, for instance, by a flow meter, which may be positioned upstream of a junction where the volume flows diverge. A flow meter is understood to be either a volumetric flow meter or a mass flow meter.

[0023] Each of the supply lines assigned to a fuel cell unit can have a valve. By controlling these valves, the amount of air allocated to a single fuel cell unit can be regulated. (R.416988)

[0024] - 4 -

[0025] The airflows can be adjusted. This allows the air-side inflows to be controlled separately. Complete control of the cathode paths of the air as a whole, as is known from the prior art, is not achieved.

[0026] Furthermore, the method can include measuring the air flow rate in an air-side supply line, and thus upstream of the gas inlet to the fuel cell unit. Flow meters can be arranged in a path upstream of the node and / or in paths downstream of the node.

[0027] Furthermore, the method can include measuring the temperature in an air-side supply line. This can be done using flow meters located in the path assigned to the module and / or in the fuel cell unit-specific paths.

[0028] The fuel cell module can include at least one heat exchanger and / or bypass in the air-side supply line. For example, a heat exchanger and / or a bypass, which may include a valve, can be provided in the fuel cell unit-specific paths of the air-side supply line. This divides the supply line into a main path and a bypass. The flow rate in the bypass can be adjusted via a valve. A valve can also be provided in the main path. A flow meter can be provided in both the main path and the bypass to determine the respective flow rates. The heat exchanger exchanges heat between the air-side discharge and the air-side supply line to transfer heat to the supplied air. The bypass preferably surrounds or bypasses the heat exchanger. The bypass thus branches off in the direction of flow, particularly upstream of the heat exchanger, and subsequently rejoins the main path.

[0029] A heat exchanger and / or a bypass can also be provided in the air-side supply line upstream of the junction. Here too, the heat exchanger is bypassed as described above.

[0030] Furthermore, no valve may be provided in the individual supply lines assigned to the fuel cell units. The volume flow is thus distributed evenly among the individual fuel cell units. Individual volume flows or flow rates assigned to the fuel cell units can be R.416988

[0031] - 5 -

[0032] It cannot be affected, however the flow rate assigned to the entire module can be adjusted.

[0033] In both cases, the bypass can be configured as a separate supply line from an inlet of the module. It can therefore include a separate feed unit and / or valve. The bypass then merges with the primary supply line after the heat exchanger, as previously described. Such a second supply line can also include a junction and thus split depending on the fuel cell unit, then merge with the primary supply line after the corresponding fuel-specific heat exchangers.

[0034] The aim of the control system is to ensure that the temperature at the air outlet of the fuel cell units does not exceed a predefined temperature threshold and / or remains within a predefined temperature range, preferably between 580°C and 650°C. This is intended to prevent component damage. Furthermore, the maximum outlet temperature is defined as a temperature difference compared to the air inlet temperature. This is intended to guarantee that the battery cell units are adequately cooled by the air. In other words, the cooling capacity of the airflow is defined.

[0035] The higher the flow rate, the lower the temperature in the air-side exhaust. This means that the flow rate can be specifically adjusted to maintain the temperature values ​​mentioned above. Flow rate control in an air-side supply line is primarily based on the fuel cell unit exhibiting the highest temperature in the exhaust. Fuel cell unit-specific measurements can determine which unit has the highest air temperature in the corresponding exhaust. Control is based on the highest temperature to prevent structural damage. If adjusting the flow rate for each individual supply line assigned to a fuel cell unit is not possible, the flow rate assigned to the module itself is adjusted.Consequently, the fuel cell units that exhibited lower temperatures in the discharge receive even higher flow rates, which may lead to efficiency losses. However, these losses are accepted in consideration of potential structural damage to the fuel cell unit with the highest temperature. R.416988.

[0036] - 6 -

[0037] Furthermore, the temperature of the air in an air supply line can be measured. Temperature measurement in the supply line can take place in the path of the supply line assigned to the module upstream of the node and / or in the individual paths assigned to the fuel cell units, in which at least one corresponding temperature sensor can be located. As described above, the fuel cell module can include at least one bypass in the air supply line. Depending on the measured temperature, the flow rate of the air supplied to the bypass can then be controlled. As described above, a corresponding bypass can be provided both in the path of the air supply line upstream of a corresponding node and in the individual paths of the air supply line to the individual fuel cell units.

[0038] The purpose of the control system is to ensure that the air temperature at the air inlet does not fall below a predefined temperature threshold and / or remains within a predefined temperature range, preferably between 500°C and 800°C, and particularly preferably between 500°C and 600°C. The control system is intended to guarantee that the air temperature meets the above parameters in order to achieve sufficient cooling.

[0039] To ensure the desired temperature input at the air-side inlet of the cathode, the flow rate through the bypass can be adjusted. Because the bypass surrounds the heat exchanger, the air temperature can be effectively controlled by adjusting the ratio of the flow rates in the main path and the bypass.

[0040] Furthermore, an additional heating element, such as an electric or thermal heater, can be installed in both the main path and the bypass. If the heat input via the heat exchanger is insufficient, supplemental heating can be provided. Alternatively, a suitable heating element can be integrated into the heat exchanger. The disadvantage of a heating element in the main path is the resulting additional pressure drop, which must be compensated for by the feed unit and / or the valve. R.416988

[0041] - 7 -

[0042] The control system is preferably based on the lowest temperature in the supply line, and thus primarily on the fuel cell unit exhibiting the lowest temperature in its supply line. Fuel cell unit-specific measurements can determine which unit has the lowest air temperature in its respective supply line. If individual adjustments to the supply lines assigned to the fuel cell units are not possible, the control system ensures that the temperature in the supply line of the fuel cell unit with the lowest temperature is sufficiently high. This may result in the other fuel cell units receiving air at a higher temperature than necessary, but this is accepted as a consequence.

[0043] Furthermore, the method preferably includes measuring the oxygen concentration. It is intended to ensure that the cathode is supplied with sufficient oxygen to guarantee the electrochemical conversion. For this purpose, an O₂ sensor can be arranged in the air-side discharge, for example, in the paths assigned to the fuel cell units. The O₂ sensors are primarily lambda sensors. The fuel cell module can include at least one recirculation path between the air-side discharge and the air-side supply line. The recirculation path is understood to be a connection between the discharge and the supply line. The flow rate of the air supplied to the supply line via the recirculation path can be controlled. The recirculation path serves, in particular, to remove contaminants from the air side or to limit their introduction.

[0044] The control of the air supplied to the recirculation path is carried out in such a way as to avoid an excessively low oxygen content in the air-side discharge.

[0045] In particular, a recirculation path between the air-side discharge and the air-side supply is controlled based on at least one oxygen concentration; specifically, the corresponding flow rate of the air supplied to the supply line via the recirculation path is controlled. R.416988

[0046] - 8 -

[0047] For example, both the recirculation path and the air-side discharge can include a valve, with both valves together influencing the air flow rate in the recirculation path.

[0048] A valve can also be located in the air-side supply line, upstream of the recirculation path, in which case no valve can be provided within the recirculation path itself. The air flows in after the valve and before the supply unit, so the supply unit determines the total volume, and the valve defines the amount of fresh air. The remaining air enters via the recirculation path.

[0049] Furthermore, a feed unit can also be provided in the recirculation path, so that both feed units, the one in the air-side supply line as well as the one in the recirculation path, determine the ratio of the flow rates.

[0050] Each of the control steps mentioned above can preferably be implemented as a control system, so that parameters such as flow rates are adjusted based on the measured values ​​to approximate the previously defined setpoints as closely as possible. In particular, the flow meters serve to determine the current flow rates and provide feedback, which can be used especially for a closed-loop control process. This allows for monitoring of the fuel cell units of the fuel cell module or the individual fuel cell units.

[0051] In principle, all of the aforementioned sensors can be integrated into components. For example, temperature and O2 sensors can be used as a single component. Valves and flow meters can also be combined into a single component.

[0052] In another aspect, the invention relates to a method for controlling a fuel cell system with at least two fuel cell modules, wherein each fuel cell module is controlled independently of the others according to a method described above. The system can incorporate fuel cell modules of different power classes, with the air-side fluidic control being independent of the other modules. R.416988

[0053] this is done and thus ensures safe, efficient and long-lasting operation at the module level.

[0054] The invention also relates to a fuel cell module comprising at least two fuel cell units, each fuel cell unit comprising an air inlet and an air outlet. Each fuel cell unit has an associated temperature sensor for measuring the temperature of the air downstream of the air outlet in an air-side duct. Furthermore, the fuel cell module includes a control unit for controlling the fuel cell module based on the measured temperatures. The invention may also relate to a system comprising several such fuel cell modules.

[0055] The invention provides a holistic, cost-effective and highly efficient concept for cathode-side or air-side control within a fuel cell module.

[0056] They show, in purely schematic form:

[0057] Figure 1: a method for controlling a fuel cell module;

[0058] Figure 2: a method for controlling a fuel cell system with at least two fuel cell modules;

[0059] Figure 3: a fuel cell module with at least two fuel cell units;

[0060] Figure 4: a fuel cell module with at least two fuel cell units;

[0061] Figure 5: a fuel cell module with at least two fuel cell units.

[0062] Figure 1 shows a method 100 for controlling a fuel cell module comprising several fuel cell units. The temperature in an air-side duct downstream of the air outlet of each fuel cell unit is measured using temperature sensors assigned to the respective fuel cell units. R.416988

[0063] - 10 -

[0064] The control process 102 is now carried out depending on the measured temperatures. Specifically, the method can include controlling 103 the air flow rate in an air-side supply line as a function of the temperatures. The air flow rate can be controlled in a path of the supply line assigned to the fuel cell module. Furthermore, the flow rate can be controlled in the paths assigned to the fuel cell units. In detail, a feed unit and / or a valve in the air-side supply line can be controlled to change the flow rate 104. For monitoring purposes, the air flow rate in the air-side supply line assigned to the fuel cell unit and / or the fuel cell module can be measured 105.

[0065] Furthermore, the method 100 can include measuring 110 the temperature of the air in the air-side supply line associated with a fuel cell unit and / or a supply line associated with the fuel cell module, and controlling 111 the flow rate of the air supplied to a bypass in the air-side supply line depending on the measured temperature. The bypass bypasses a heat exchanger between the air-side supply line 70a and the air-side discharge 70b. Furthermore, the method 100 can include heating 120 air in the air-side supply line by means of a further heating element in the bypass and / or in the main path bypassed by the bypass. Furthermore, the method 100 can include controlling 121 the flow rate of air that is directed from the air-side discharge to the air-side supply line by means of a recirculation path.

[0066] Figure 2 shows a purely schematic method 200 for controlling a fuel cell system with at least two fuel cell modules, wherein a method 100 described above for controlling a fuel cell module is used for each module, so that the fuel cell modules can be controlled independently of each other.

[0067] Figure 3 shows a fuel cell module 10 with two fuel cell units 11, namely a first fuel cell unit 11a and a second fuel cell unit 11b. Each fuel cell unit 11 has an anode 12 with a gas inlet 12a and a gas outlet 12b. Furthermore, each fuel cell unit 11 has a cathode 13 with an air inlet 13a and R.416988

[0068] - 11 -

[0069] an air outlet 13b. For the cathode 13 there is therefore an air-side supply line 70a.

[0070] The air-side supply line 70a extends to the air inlet 13a of the respective fuel cell unit, and the air-side discharge line 70b extends from the air outlet 13b. Starting from the lower end of Figure 3, the air-side supply line 70a is initially assigned to both fuel cell units 11 and thus to the fuel cell module 10. This is the fuel cell module-specific path of the supply line, whereby, after a junction 35, it divides into air-side supply lines assigned to the individual fuel cell units 11. The air-side discharge line 70b is also assigned to the entire fuel cell module 10 from a junction 35 onwards, whereas previously it was assigned to the individual fuel cell units.

[0071] Fuel gas is supplied to the anode 12 via a fuel gas supply line 21a. The fuel gas supply line 21a extends to the gas inlet 12a, and the fuel gas outlet 21b extends from the gas outlet 12b. The fuel gas supply line 21a runs in a path assigned to the fuel cell module 10 up to a node 35, and from node 35 onwards, it runs in paths assigned to individual fuel cell units. The fuel gas outlet 21b initially runs from the fuel cell units in individual specific paths and from node 35 onwards in a common path.

[0072] Several temperature sensors 40 are arranged in the air-side duct 70b. As shown in Figure 3, a temperature sensor 40b is preferably arranged directly behind the air outlet 13b for each fuel cell unit 11, enabling it to measure the temperature directly after the air outlet 13b. An O2 sensor 95 can also be provided at a corresponding location. Another O2 sensor 95 can then be installed downstream of a junction 35 in the common path of the air-side duct 70b, so that it measures the mixed temperature of the air coming from the fuel cell units 11. Further temperature sensors 40b can also be arranged in this path, for example, upstream and downstream of a heat exchanger 50, which connects to the air-side duct 70b and the air-side supply line.

[0073] - 12 -

[0074] 70a is integrated to transfer heat from the exhausted air to the supplied air.

[0075] A feed unit 25 can be arranged at the beginning of the air-side supply line 70a. A temperature sensor 40a and a flow meter 30 can follow to measure the air flow rate at the corresponding point.

[0076] Several temperature sensors 40a can be arranged in the air-side supply line 70a, for example, upstream and / or downstream of a bypass 60. The bypass 60 is located in the supply line 70a upstream of a junction 35 where the supply line splits to the fuel cell units 11. A further flow meter 30 can be provided in the bypass 60 to measure the flow rate within the bypass 60. A second valve 62 can also be provided in the bypass 60. A first valve 61 can be located in the portion of the main path bypassed by the bypass 60. The bypass 60 bridges the heat exchanger 50. A heating element 45 can also be arranged in the bypass 60.

[0077] Figure 3 also schematically depicts a control unit 80 with a first control module 80a and a second control module 80b. The fuel cell module 10 can be controlled based on the measured temperatures in the air-side exhaust. The figure illustrates how the feed unit 25 can be controlled to change the air flow rate in the air-side supply line 70a.

[0078] Based on at least one temperature measurement in the air-side supply line 70a, the flow rate of the air supplied to the bypass 60 is controlled, for example, by controlling the first valve 61 and / or the second valve 62. Furthermore, the heating element 45 can be used to increase the temperature of the air. The heating element 45 can also be located at other points, for example, in the main path downstream of the heat exchanger 50, that is, after the bypass 60 has rejoined the main path, and upstream of the junction 35 where the air is distributed to the individual fuel cell units.

[0079] - 13 -

[0080] Figures 4a to 4c show fuel cell modules 10 which, apart from the following differences, are designed analogously to Figure 3:

[0081] In bypass 60, no heating element 45 is shown here. Furthermore, the fuel cell module 10 now includes a recirculation path 91 to the air-side supply line 70a, so that air is directed from the outlet 70b to the supply line 70a.

[0082] In Figure 4a, the recirculation path 91 begins upstream of a valve 92 in the air-side duct 70b and downstream of the O2 sensor 60a. The recirculation path 91 also includes a valve 92 and a flow meter 30, and is then fed (in the direction of flow of the supply line) upstream of the supply unit 25 of the supply line 70a. The two valves 92 determine the flow rate and thus the proportion of air supplied via the recirculation path 91, while the supply unit 25 determines the total amount of air supplied to the air-side supply line 70a.

[0083] In the configuration shown in Figure 4b, the recirculation path 91 has no valve, but, as in Figure 4a, the flow meter 30. Furthermore, an additional valve 92 is provided in the air-side supply line 70a upstream of the feed unit 25. The feed unit 25 defines the overall flow rate, with the valve 92 determining the inflow of fresh air, while the remainder originates from the recirculation path 91.

[0084] In the third configuration of Figure 4c, another feed unit 25 is inserted into the recirculation path 91. The flow rate is determined by the feed units 25.

[0085] Figure 5 shows a fuel cell module 10 with two fuel cell units 11, namely a first fuel cell unit 11a and a second fuel cell unit 11b, wherein the fuel cell units 11 are designed analogously to the previous figures.

[0086] Again, a fuel gas supply line 21a, a fuel gas outlet 21b, an air supply line 70a and an air outlet 70b are provided. A feed unit 25 is again provided in the air supply line 70a and a flow meter 30 in the path of R.416988 assigned to the fuel cell module.

[0087] - 14 -

[0088] air-side supply line 70a. The flow meter 30 thus measures the total flow rate assigned to the module.

[0089] Furthermore, a flow meter is arranged in each of the fuel cell unit-specific supply lines 70a. The individual flow rates to the fuel cell units 11 can thus be measured using these flow meters.

[0090] Furthermore, a bypass 60 is provided for each fuel cell unit 11, each with a second valve 62. A first valve 61 can again be provided in the main path. The bypass 60 again spans both the first valve 61 and the heat exchanger 50. Several temperature sensors 40a can be provided in the air-side supply line, either upstream of the bypass 60, downstream of it, or in the main path that is bypassed by the bypass. Several temperature sensors 40b can also be arranged in the air-side outlet 70b. Furthermore, an O2 sensor 95 is provided in the air-side outlet 70b assigned to each fuel cell unit 11, upstream of a junction 35. Finally, an O2 sensor is installed in a common outlet 70b for all fuel cell units 11.

Claims

R.416988 - 15 - Claims 1. Method (100) for controlling a fuel cell module (10) comprising at least two fuel cell units (11), wherein each fuel cell unit (11) comprises an air inlet (13a) and an air outlet (13b), characterized by the fact that the procedure (100) comprising a measurement (101) of the respective temperature of the air in an air-side duct (70b) after the air outlet (13b) of each fuel cell unit (11) by means of a temperature sensor (40) assigned to the fuel cell unit and a control (102) of the fuel cell module (10) depending on the measured temperatures.

2. Method (100) according to claim 1 , characterized by the fact that the method (100) comprises a control (103) of an air flow rate in an air-side supply line (70a) depending on the measured temperatures 3. Method (100) according to claim 2, characterized by the fact that the supply line includes a feed unit (25) and / or at least one valve (92) for controlling the flow rate, wherein the method (100) comprises a control (104) of the feed unit (25) and / or of the at least one valve (92).

4. Method (100) according to claim 2 or 3, characterized by the fact that the procedure (100) comprises measuring (105) a flow rate of air in an air-side supply line (70a).

5. Method (100) according to one of the preceding claims, characterized in that R.416988 - 16 - the method (100) comprises measuring (110) the temperature of the air in an air-side supply line (70a).

6. Method (100) according to claim 5, characterized by the fact that the fuel cell module (11) includes at least one bypass (60) of the air-side supply line (70a), wherein the method (100) comprises a control (111) of a flow rate of the air supplied to the bypass (60) as a function of the measured temperature 7. Method (100) according to claim 5 or 6, characterized by the fact that the bypass (60) bridges a heat exchanger (50) arranged in the air-side supply line (70a), wherein the method (100) comprises heating (120) air in the air-side supply line (70a) by means of a further heating element (45) in the bypass (60) and / or a main path of the air-side supply line (70a) 8. Method (100) according to claim 7, characterized by the fact that the fuel cell module (10) includes at least one recirculation path (91) between the air-side discharge (70b) and the air-side supply line (70a), wherein the method (100) comprises a control (121) of a flow rate of the air supplied to the supply line (70a) via the recirculation path (91).

9. Method (200) for controlling a fuel cell system with at least two fuel cell modules (10), characterized by the fact that Each fuel cell module (10) is controlled independently of each other according to one of the methods (100) of claims 1 to 8.

10. Fuel cell module (10) comprising at least two fuel cell units (11), R.416988 - 17 - wherein each fuel cell unit (11) comprises an air inlet (13a) and an air outlet (13b), characterized by the fact that Each fuel cell unit (11) includes one of these associated temperature sensors (40) for measuring a respective temperature in an air-side duct (70b) downstream of the air outlet (11b) of the fuel cell unit (11), wherein the fuel cell module (10) comprises a control unit (80) for controlling the fuel cell module (10) depending on the measured temperatures

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