Fuel recirculation in a fuel cell device having multiple fuel cell stacks

Abstract

The invention relates to a fuel cell device (1) comprising: a fuel tank (2) having a fuel supply line (3) branching off to form partial fuel supply lines (4); a plurality of fuel cell stacks (5) each having a fuel connection (6) on the anode inlet side, each of which is fluidically connected to one of the partial fuel supply lines (4). Only one of the fuel cell stacks (5) is connected to a fuel recirculation line (7) on the anode outlet side, the flow guidance of the fuel recirculation line (7) being selected such that fuel can only be returned to the fuel cell stack (5) connected to the fuel recirculation line (7). The invention also relates to a method for operating the fuel cell device (1).

Description

Technical Field

[0001] The present invention relates to a fuel cell system comprising: a fuel tank having a fuel supply line branching off to form partial fuel supply lines; and a plurality of fuel cell stacks, each of which has a fuel connection on the anode inlet side that is fluidically connected to one of the partial fuel supply lines. The present invention also relates to a method for operating the fuel cell system. Background Art

[0002] Fuel cells are used to supply energy, particularly in motor vehicles. To provide the required amount of energy, multiple fuel cells are arranged in a fuel cell stack. High power is required to power commercial vehicles, so fuel cell systems for commercial vehicles preferably include multiple fuel cell stacks. Individually operating and controlling these multiple fuel cell stacks requires a complex system of individual reactant supply lines and exhaust gas lines. Efficient fuel utilization also requires a complex system of fuel recirculation lines, which are fluidically connected to the individual fuel cell stacks. This results in high costs and complex system operation.

[0003] CN 110 828 857A and KR 2006 0024 900A each disclose a fuel cell device having a plurality of fuel cell stacks, each having a central fuel recirculation line, wherein the central fuel recirculation line is fluidically and mechanically connected to each fuel cell stack. WO 2007 / 087240 A2 discloses a plurality of fuel cell stacks in a fuel cell device, wherein each fuel cell stack has a fuel recirculation line fluidically and mechanically connected to a fuel supply line.

[0004] DE 10 2018 218 638 A1 shows a fuel cell system with a plurality of fuel cell stacks. A fuel supply line branches off to form a plurality of partial fuel supply lines, wherein each fuel cell stack is fluidically connected to a fuel recirculation line.

[0005] EP 0 269 877 A1, DE 10 2006 051 433 A1 and US 2010 / 047 641 A1 each disclose a fuel recirculation system in which a plurality of fuel cells are connected in series and one of the fuel cell stacks is fluidically connected to a fuel recirculation line. Summary of the Invention

[0006] It is therefore an object of the present invention to provide a fuel cell system and a method for operating a fuel cell system which generate high power and have reduced system complexity.

[0007] The objects related to the fuel cell arrangement are achieved by the fuel cell arrangement according to the invention. The objects related to the method for operating a fuel cell arrangement are achieved by the method according to the invention. The invention comprises a number of advantageous embodiments, which have advantageous developments of the invention.

[0008] The fuel cell device is characterized in that only one of the fuel cell stacks is connected to the fuel recirculation line on the anode outlet side. The flow guidance of the fuel recirculation line is selected so that the fuel can only be fed back into the fuel cell stack connected to the fuel recirculation line. Therefore, the fuel recirculation is significantly simplified by supplying the recycled fuel to only one stack. This simplification also reduces costs and the space required for fuel recirculation within the fuel cell device. It is also provided that the fuel cell device has only a single purge valve (Purgeventil) in the fuel recirculation line. In other words, it is sufficient for the fuel cell device to have exactly one purge valve. This also reduces costs and complexity. Similarly, the fuel cell device preferably has only one delivery mechanism in the fuel recirculation line. This delivery mechanism can be in the form of a jet pump or a recirculation fan.

[0009] It is particularly advantageous if there are a number of flow paths corresponding to the number of fuel connections, each flow path leading from the fuel tank via the fuel supply line and via one of the partial fuel supply lines to one of the fuel connections, and only the last fuel cell stack with the longest flow path is connected to the fuel recirculation line. If only the last of the fuel cell stacks is connected to the fuel recirculation line, then the other fuel cell stacks located flow-wise upstream of the last fuel cell stack have improved operation because they are supplied with pure fuel. Consequently, for these other fuel cell stacks, i.e., those not connected to the fuel recirculation line, a higher fuel partial pressure can be achieved, thereby enabling higher cell voltages and efficiencies.

[0010] In an alternative embodiment, there are a number of flow paths corresponding to the number of fuel connections, each of which leads from the fuel tank via the fuel supply line and via one of the partial fuel supply lines to one of the fuel connections, and only the first fuel cell stack with the shortest flow path is connected to the fuel recirculation line. This also has the advantage that the other fuel cell stacks located flow-wise downstream of the first fuel cell stack are supplied with pure fuel and have improved operation or a higher fuel partial pressure. This allows the other fuel cell stacks to achieve higher cell voltages and efficiencies.

[0011] Furthermore, it is advantageous if the fuel recirculation line is fluidically connected to a portion of the fuel supply line of the fuel cell stack that is connected to the fuel recirculation line. This allows efficient refeeding of fuel into the anode chamber of the fuel cell stack that is connected to the fuel recirculation line.

[0012] However, it is also possible in principle to connect one of the other fuel cell stacks, ie neither the first nor the last, to the fuel recirculation line.

[0013] In order to optimize fuel utilization and increase efficiency in the other fuel cell stack, it is useful to connect the other fuel cell stack to one of the partial fuel supply lines of the adjacent fuel cell stack in terms of flow technology at the anode outlet side. This increases the hydrogen partial pressure within the other fuel cell stack and improves the efficiency of the other fuel cell stack.

[0014] A method for operating a fuel cell system, characterized by the following steps:

[0015] a) activating a fuel cell stack connected to a fuel recirculation line by supplying reactants;

[0016] b) operating the fuel cell arrangement with at least the fuel cell stack connected to a fuel recirculation line; and

[0017] c) Deactivating the fuel cell stack connected to the fuel recirculation line by cutting off the supply of reactants.

[0018] In other words, the fuel cell stack with the fuel recirculation line is always activated first. This allows for safe and efficient operation of the fuel cell system while making optimal use of the available fuel.

[0019] It is also advantageous if, after the fuel cell stack connected to the fuel recirculation line has been activated, at least one additional fuel cell stack is activated only when the fuel cell system is switched on, by supplying reactants and electrically connecting at least one additional fuel cell stack to the at least one already activated fuel cell stack. This allows the fuel cell system to be operated with multiple fuel cell stacks, thereby enabling the high power required, for example, when implementing the fuel cell system in commercial vehicles. This also allows the individual fuel cell stacks to be activated independently of one another depending on the power required.

[0020] In this regard, it is preferred that, before deactivating the fuel cell stack connected to the fuel recirculation line, the other fuel cell stacks are first deactivated when the fuel cell system is shut down by shutting off the reactant supply and electrically disconnecting the other fuel cell stacks. In this case, it is also possible to deactivate individual fuel cell stacks according to the required power, so that a corresponding number of fuel cell stacks in the fuel cell system are activated or deactivated depending on the power required by the vehicle.

[0021] Furthermore, it is advantageous to operate at least one of the other fuel cell stacks at a higher fuel pressure than the fuel cell stack connected to the fuel recirculation line. In particular, when the last fuel cell stack is connected to the fuel recirculation line, it is provided that the first fuel cell stack having the shortest flow path of all flow paths is operated at a higher fuel pressure than the last fuel cell stack having the longest flow path of all flow paths. Conversely, it is advantageous to operate the last fuel cell stack having the longest flow path of all flow paths at a higher fuel pressure than the first fuel cell stack having the shortest flow path of all flow paths when the first fuel cell stack is connected to the fuel recirculation line. This allows for optimal efficiency in the operation of the fuel cell system.

[0022] Furthermore, in this regard, it is provided that the fuel pressure of at least one other fuel cell stack is selected such that the fuel pressure of the other fuel cell stack on the anode outlet side corresponds to the fuel pressure of the fuel cell stack connected to the fuel recirculation line on the anode outlet side. If the last fuel cell stack of the fuel cell stack is connected to the fuel recirculation line, it is particularly provided that the fuel pressure of the first fuel cell stack having the shortest flow path of all flow paths is selected such that the fuel pressure of the first fuel cell stack on the anode outlet side corresponds to the fuel pressure of the last fuel cell stack having the longest flow path of all flow paths on the anode outlet side. In an alternative embodiment, when the first fuel cell stack of the fuel cell stack is connected to the fuel recirculation line, it is advantageous if the fuel pressure of the last fuel cell stack having the longest flow path of all flow paths is selected such that the fuel pressure of the last fuel cell stack on the anode outlet side corresponds to the fuel pressure of the first fuel cell stack having the shortest flow path of all flow paths on the anode outlet side. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further advantages, features and details of the present invention are apparent from the following description of preferred embodiments with reference to the accompanying drawings.

[0024] Figure 1 A fuel cell arrangement having a plurality of fuel cell stacks is shown. DETAILED DESCRIPTION

[0025] Fuel cells are used to generate energy and can in particular be used to generate energy for driving a motor vehicle. In this case, a plurality of fuel cells are preferably combined in a fuel cell stack 5 .

[0026] Each fuel cell comprises an anode, a cathode and a proton-conducting polymer membrane separating the anode from the cathode. The polymer membrane is formed of an ionomer, preferably a sulfonated tetrafluoroethylene polymer (PTFE) or a perfluorosulfonic acid polymer (PFSA). Alternatively, the polymer membrane can be formed as a sulfonated hydrocarbon membrane.

[0027] Catalysts can also be mixed into the anode and / or cathode, wherein the membrane is preferably coated on its first side and / or its second side with a catalyst layer consisting of a noble metal or a mixture containing noble metals such as platinum, palladium, ruthenium, etc., which serve as reaction promoters in the reactions of the corresponding fuel cell.

[0028] Fuel (e.g., hydrogen) can be supplied to the anode through the anode compartment. In a polymer electrolyte membrane fuel cell (PEM fuel cell), the fuel or fuel molecules are split into protons and electrons at the anode. PEM allows protons to pass through, but not electrons. For example, the reaction at the anode is: 2H2 → 4H + +4e - (Oxidation / electron release). While the protons pass through the PEM to the cathode, the electrons are directed to the cathode or energy storage device through an external circuit.

[0029] Cathode gas (e.g., oxygen or oxygen-containing air) can be supplied to the cathode through the cathode chamber, so that the following reaction occurs on the cathode side: O2 + 4H + +4e - →2H2O (reduction / electron absorption).

[0030] In order to ensure ionic conductivity for hydrogen protons through the PEM, the presence of water molecules in the PEM is required. Therefore, in particular the cathode gas is humidified before it is supplied to the fuel cell in order to cause water saturation of the PEM.

[0031] Figure 1 A fuel cell system 1 is shown, comprising a plurality of fuel cell stacks 5, 9, 10, 11 and a fuel tank 2. This fuel cell system 1 can be used, for example, in commercial vehicles to generate high power. The fuel tank 2 has a fuel supply line 3, which branches to form partial fuel supply lines 4. Each of the plurality of fuel cell stacks 5, 9, 10, 11 has a fuel connection 6 on the anode inlet side. Fuel valves 13, corresponding in number to the number of partial fuel supply lines 4, are connected to the partial fuel supply lines 4. These fuel valves enable the individual fuel cell stacks 5, 9, 10, 11 to be supplied with fuel independently of one another, i.e., to be operated independently of one another.

[0032] Furthermore, there are a number of flow paths corresponding to the number of fuel connections 6. Each flow path leads from the fuel tank 2 via the fuel supply line 3 and via one of the partial fuel supply lines 4 to one of the fuel connections 6. In the present embodiment, only the last of the fuel cell stacks 9, 5 having the longest flow path is connected to the fuel recirculation line 7. Figure 1 As can be seen, this has the advantage that the entire fuel cell system 1 has only one fuel recirculation line 7, which also requires only one delivery mechanism 8 and also only one discharge valve 12. The delivery mechanism 8 can be designed as a jet pump or a recirculation fan. The fuel is guided back by the delivery mechanism via the fuel recirculation line 7 only to the fuel supply line 4 of the fuel cell stack 5 connected to the fuel recirculation line 7.

[0033] In an embodiment not shown, it is also possible that not the last of the fuel cell stacks 5 , 9 but the first of the fuel cell stacks 5 , 10 having the shortest flow path is connected to the fuel recirculation line 7 .

[0034] The other fuel cell stacks 11 , 5 are fluidically connected on the anode outlet side to one of the partial fuel supply lines 4 of the adjacent fuel cell stack 5 . This results in a pressure increase of the fuel pressure in the respective fuel cell stack 5 , 9 , 10 , 11 .

[0035] In addition to a separate fuel connection 6 for supplying fuel to the anode space, each fuel cell stack also has a separate cathode gas connection for supplying cathode gas to the cathode space of the fuel cell stack 5. The cathode gas connection is connected to a cathode supply line 14, which leads from a compressor 15 via a charge air cooler and a humidifier 16 to the fuel cell stacks 9, 10, and 11. A cathode exhaust line 19 is also provided, which leads to the humidifier 16. The cathode gas is drawn in by the respective compressor 15, compressed by it, and passed via the cathode supply line 14 and the charge air cooler 17 to the humidifier 16.

[0036] The method for operating the fuel cell system 1 is as follows: When the fuel cell system 1 is switched on, the fuel cell stack 5 connected to the fuel recirculation line 7 , ie the last of the fuel cell stacks 9 , 5 in this embodiment, is first activated by supplying the reactants, ie the fuel and the cathode gas.

[0037] After activation of the fuel cell stack 5 connected to the fuel recirculation line 7, at least one further fuel cell stack 11, 5 is activated, if necessary, by supplying reactants and electrically connecting at least one further fuel cell stack 5, 11 to the at least one already activated fuel cell stack 5. The at least one further fuel cell stack 11, 5 is preferably operated at a higher fuel pressure than the fuel pressure of the fuel cell stack 9, 5 connected to the fuel recirculation line 7. The fuel pressure is selected such that the anode outlet-side fuel pressure of the at least one further fuel cell stack 11, 5 corresponds to the anode outlet-side fuel pressure of the fuel cell stack 5, 9 connected to the fuel recirculation line 7. The fuel cell system 1 is now operated with the activated fuel cell stacks 5, 9, 10, 11.

[0038] By individually activating the fuel cell stacks 5, 9, 10, 11, it is possible to operate the fuel cell system 1 according to the required power. When the fuel cell system 1 is shut down, before the fuel cell stack 9, 5 connected to the fuel recirculation line 7 is deactivated by shutting off the supply of reactants, the other fuel cell stacks 11, 5 are first deactivated by shutting off the supply of reactants and by electrically disconnecting the other fuel cell stacks 11, 5.

[0039] List of Reference Numerals

[0040] 1. Fuel cell device

[0041] 2 fuel tanks

[0042] 3 fuel supply lines

[0043] 4-part fuel supply lines

[0044] 5. Fuel cell stack

[0045] 6 Fuel connection

[0046] 7Fuel recirculation line

[0047] 8 conveying mechanism

[0048] 9The last fuel cell stack

[0049] 10The first fuel cell stack

[0050] 11Other fuel cell stacks

[0051] 12 Exhaust valve

[0052] 13 Fuel valve

[0053] 14 cathode supply line

[0054] 15 compressor

[0055] 16. Humidifier

[0056] 17 Charge air cooler

[0057] 18 Humidifier discharge line

[0058] 19 cathode discharge line.

Claims

1. A fuel cell device (1) comprising: a fuel tank (2) having a fuel supply line (3) which is configured to branch into partial fuel supply lines (4); a plurality of fuel cell stacks (5), each of which has a fuel connection part (6) on the anode inlet side, each of which is fluidically connected to one of the partial fuel supply lines (4), characterized in that Only one of the fuel cell stacks (5) is connected to a fuel recirculation line (7) on the anode outlet side, while the other fuel cell stacks (11, 5) in the fuel cell stack are flow-technically connected to one of the partial fuel supply lines (4) of an adjacent fuel cell stack (5) on the anode outlet side, and the flow guidance of the fuel recirculation line (7) is selected so that the fuel can only return to the fuel cell stack (5) connected to the fuel recirculation line (7), and a number of fuel valves (13) corresponding to the number of the partial fuel supply lines (4) are connected.

2. The fuel cell device (1) according to claim 1, characterized in that There are a number of flow paths corresponding to the number of the fuel connections (6), each of the flow paths leading from the fuel tank (2) via the fuel supply line (3) and via one of the partial fuel supply lines (4) to one of the fuel connections (6), and only the last fuel cell stack (9, 5) of the fuel cell stacks having the longest flow path is connected to the fuel recirculation line (7).

3. The fuel cell device (1) according to claim 1, characterized in that There are a number of flow paths corresponding to the number of the fuel connections (6), each of the flow paths leading from the fuel tank (2) via the fuel supply line (3) and via one of the partial fuel supply lines (4) to one of the fuel connections (6), and only the first fuel cell stack (10, 5) of the fuel cell stacks having the shortest flow path is connected to the fuel recirculation line (7).

4. The fuel cell device (1) according to any one of claims 1 to 3, characterized in that The fuel recirculation line (7) is fluidically connected to a portion of the fuel supply line (4) of the fuel cell stack (5), which is coupled to the fuel recirculation line (7).

5. A method for operating a fuel cell device (1) according to any one of claims 1 to 4, comprising the following steps: a) activating a fuel cell stack (5) coupled to the fuel recirculation line (7) by supplying reactants; b) operating the fuel cell device (1) with at least the fuel cell stack (5) connected to the fuel recirculation line (7); and c) deactivating the fuel cell stack (5) coupled to the fuel recirculation line (7) by cutting off the supply of reactants.

6. The method according to claim 5, characterized in that When the fuel cell device (1) is turned on, the at least one other fuel cell stack (11, 5) is activated only after the fuel cell stack (5) connected to the fuel recirculation line (7) is activated by supplying the reactants and by electrically connecting the at least one other fuel cell stack (11, 5) to the at least one already activated fuel cell stack (5).

7. The method according to claim 6, characterized in that When the fuel cell device (1) is shut down, the other fuel cell stacks (11, 5) are first deactivated by cutting off the supply of reactants and by electrically disconnecting the other fuel cell stacks (11, 5) before deactivating the fuel cell stack (5) connected to the fuel recirculation line (7).

8. The method according to claim 6 or 7, characterized in that At least one of the other fuel cell stacks (11, 5) operates at a higher fuel pressure than the fuel cell stack (5) connected to the fuel recirculation line (7).

9. The method according to any one of claims 6 to 7, characterized in that The fuel pressure of at least one of the other fuel cell stacks (11, 5) is selected such that the fuel pressure of the other fuel cell stack (11, 5) on the anode outlet side corresponds to the fuel pressure of the fuel cell stack (5) connected to the fuel recirculation line (7) on the anode outlet side.

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