Air system for a fuel cell system, fuel cell system

Abstract

The invention relates to an air system (1) for supplying several fuel cell stacks (2) with air, comprising - a main supply air path (3) which branches into several secondary supply air paths (4.1, 4.2), and - an air compression system (5) with a first compression stage (5.1) and a second compression stage (5.2), wherein the second compression stage (5.2) comprises a plurality of air compressor units (6), each of which is arranged in a secondary supply air path (4.1, 4.2) and is coupled to a turbine (8) arranged in an exhaust air path (7) as the sole drive, wherein a combustion chamber (9) for the oxidation of hydrogen is integrated in each of the exhaust air paths (7) upstream of the turbines (8), which can be fed to the combustion chambers (9) via a connecting line (11) connected to an anode subsystem (10).

Description

[0001] The invention relates to an air system for a fuel cell system and to a fuel cell system with an air system according to the invention. The fuel cell system comprises several fuel cell stacks that are supplied with air via the air system ("multi-stack system").

[0002] The preferred field of application of the invention is mobile fuel cell systems or vehicles in which drive energy is generated by several fuel cell stacks or stacks. State of the art

[0003] In vehicles where drive energy is supplied by one or more fuel cell stacks or fuel cell systems, the oxidant oxygen from the ambient air is generally used to react with hydrogen in the fuel cell to form water or water vapor and thus produce electrical power through electrochemical conversion. The ambient air is fed to the fuel cell stack via an air conveying system or air compression system, since the electrochemical conversion requires a certain air mass flow and a certain pressure level. The air is usually compressed using a thermal turbomachine driven by an electric motor. Optionally, energy can be recovered from the outflowing moist air using a turbine for air compression. The exhaust gas enthalpy is used to drive a compressor wheel via the turbine.

[0004] Higher system pressures generally require multi-stage air compression and energy recovery via a turbine. State-of-the-art air compression systems employ multiple shafts or shaft-rotor units connected in series, at least one of which is combined with a turbine.

[0005] The electrical power requirement of an air compression system in a fuel cell system is considerable and represents by far the largest parasitic consumer. This is because the electrical power must be additionally supplied by at least one fuel cell stack. This increases the gross power required to achieve a desired net / useful power. Stack dimensions and system costs increase accordingly. The increased gross power also leads to increased cooling requirements for both the stack and the air compressor unit. In mobile applications, however, the cooling capacity is limited, so that the stack power may need to be derated, especially at very high ambient temperatures. Elevated temperatures, in turn, accelerate stack aging.

[0006] In a fuel cell system comprising multiple fuel cell stacks (“multi-stack system”), air compressor systems are typically required that feature several air compressor units connected in series to achieve multi-stage compression. Each air compressor unit, in turn, requires very expensive power electronics, resulting in high costs.

[0007] The present invention is concerned with the task of reducing or eliminating the disadvantages of the prior art. To achieve this task, the air system having the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the subclaims. Furthermore, a fuel cell system with an air system according to the invention is specified. Disclosure of the invention

[0008] An air system is proposed for supplying air to multiple fuel cell stacks. The air system includes: - a main supply air path that branches into several secondary supply air paths, and - an air compression system with a first compression stage and a second compression stage, wherein the second compression stage comprises a plurality of air compressor units, each of which is arranged in a secondary supply air path and is coupled to a turbine arranged in an exhaust air path as the sole drive.

[0009] A combustion chamber for the oxidation of hydrogen is integrated into the exhaust air paths upstream of the turbines, which can be fed to the combustion chambers via a connecting line connected to an anode subsystem.

[0010] Turbine-driven air compressor units of the second compression stage with an upstream combustion chamber are referred to below as "GTAC" for simplicity. Air compressor units that are driven purely by electric motors are referred to below as "EAC." If a turbine is also provided as a drive, the term "EACT" is used below.

[0011] The proposed air system with multi-stage air compression therefore includes a second compression stage consisting of several GTACs. Since each GTAC is located in its own secondary supply air path, the GTACs are connected in parallel. The parallel GTACs are jointly supplied via the main supply air path with air that has already been pre-compressed by the first compression stage of the air compression system. This has the following advantages: - Reduction of the electrical power of the fuel cell stacks by significantly reducing the parasitic loads, in particular by reducing the size of the fuel cell stacks and / or increasing the stack efficiencies; - Reduction of thermal waste heat from the fuel cell stacks, which allows for a reduction in the size of the cooling system and / or a reduction in the stack operating temperature; - Improvement of stack aging by lowering the temperature, especially at high load points; - Cost savings regarding stack costs as well as costs for cooling systems, power electronics components, cabling, etc.; - Reduction of installation space requirements by reducing the size of fuel cell stacks, cooling systems, power electronics components, etc.; - Evaporation of water droplets contained in the air before entering the turbines through the upstream combustion chambers, so that the turbines are better protected against droplet impact (component protection).

[0012] In a further development of the invention, it is proposed that the first compression stage comprise at least one air compressor unit, which is arranged in the main supply air path or in a secondary supply air path and has at least one electric motor as a drive. A turbine can also be provided. The at least one air compressor unit of the first compression stage can therefore be, in particular, an EAC or an EACT.

[0013] In the EAC or EACT configuration, the at least one air compressor unit of the first compression stage serves to ensure a minimum speed that protects the gas bearings of the downstream GTACs. In this way, component protection is enhanced with the help of the at least one electric motor-driven air compressor unit. At the same time, the starting of the GTACs during a start-up process is ensured, since the air compressed by the at least one air compressor unit of the first compression stage is distributed to the air compressor units of the second compression stage via the secondary air supply paths. The at least one air compressor unit of the first compression stage also ensures that the combustion chambers upstream of the turbines are adequately supplied with air.

[0014] According to a preferred embodiment of the invention, the at least one air compressor unit of the first compression stage is arranged together with an air compressor unit of the second compression stage in a secondary air supply path. This means that the number of air compressor units in the two compression stages is the same. For example, the main air supply path can branch into two secondary air supply paths, in each of which the air compressor units of the two compression stages are arranged in series. If the secondary air supply path does not branch further, the number of fuel cell stacks is also two. Each fuel cell stack is then assigned a GTAC. However, the number of fuel cell stacks can also be a multiple of this. This requires that the secondary air supply paths branch accordingly often so that each fuel cell stack can be supplied with air via a secondary air supply path.A GTAC can then supply compressed air to multiple fuel cell stacks. By branching the main air supply path multiple times, secondary air supply paths of the first, second, and possibly third order are created.

[0015] According to a further embodiment of the invention, the at least one air compressor unit of the first compression stage is arranged in a first-order secondary air supply path, which branches into at least two second-order secondary air supply paths, each of which contains an air compressor unit of the second compression stage. By further branching the second-order secondary air supply paths, thereby creating third-order secondary air paths, multiple fuel cell stacks can be connected to a GTAC. If no further branching is provided, the number of fuel cell stacks corresponds to the number of GTACs.

[0016] Furthermore, a fuel cell system comprising a plurality of fuel cell stacks, an air system according to the invention for supplying air to the fuel cell stacks, and at least one anode subsystem for supplying the fuel cell stacks with hydrogen is proposed. The advantages of the air system also extend to the fuel cell system.

[0017] The invention and its advantages are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a first air system according to the invention in a fuel cell system, Fig. 2 a schematic representation of a second air system according to the invention in a fuel cell system, Fig. 3 a schematic representation of a third air system according to the invention in a fuel cell system, Fig. 4 a schematic representation of a fourth air system according to the invention in a fuel cell system, Fig. 5 a schematic representation of a fuel cell system according to the invention with an air system and an anode subsystem and Fig. 6 a schematic representation of another fuel cell system according to the invention. Detailed description of the drawings

[0018] Fig. 1 shows an air system 1 according to the invention for supplying air to a plurality of fuel cell stacks 2 of a fuel cell system 20. The air system 1 comprises a main supply air path 3, into which an air filter 19 and an air compressor unit 12 are integrated to form a first compression stage 5.1 of a multi-stage air compression system 5. Downstream of the air compressor unit 12, the main supply air path 3 branches into four secondary supply air paths 4, via which the fuel cell stacks 2, also four in this case, are connected to the main supply air path 3. In each of the secondary supply air paths 4, upstream of the fuel cell stacks 2, a further air compressor unit 6 is integrated to form a second compression stage 5.2 of the air compression system 5.These are each turbine-driven, with a combustion chamber 9 being connected upstream of the turbines 8 in each case, in which hydrogen is oxidized, which is made available to the combustion chambers 9 via an anode subsystem 10 of the fuel cell system 20 (analogous to the . Fig. 6). The air compressor units 6 of the second compression stage 5.2 arranged in the secondary supply air paths 4 are therefore designed as GTACs. The air compressor unit 12 of the first compression stage 5.1, on the other hand, has an electric motor 13 as drive (analogous to the Fig. 6). During operation of the air system (1), air is taken from the ambient air 18, passed through the air filter 19, and pre-compressed by the air compressor unit 12 of the first compression stage 5.1. The pre-compressed air is then distributed among the four secondary supply air paths 4, further compressed by the additional air compressor units 6 of the second compression stage 5.2 arranged therein, and fed to the fuel cell stacks 2.

[0019] Fig. 2 shows a further air system 1 according to the invention for supplying several fuel cell stacks 2 of a fuel cell system 20 with air. The air system 1 comprises a main supply air path 3, into which an air filter 19 is integrated. Downstream of the air filter 19, the main supply air path 3 branches into two first-order secondary supply air paths 4.1, in each of which an electric motor-driven air compressor unit 12 is arranged to form a first compression stage 5.1. Downstream of the air compressor units 12, the secondary supply air paths 4 each branch into two second-order secondary supply air paths 4.2, in each of which an air compressor unit 6 of the second compression stage 5.2 and a fuel cell stack 2 are arranged. Since in the Fig. 2 the first air compression stage 5.1 is formed by two air compressor units 12 connected in parallel, the system has more redundancy for high availability requirements.

[0020] Fig. Figure 3 shows an air system 1 according to the invention, in which the number of fuel cell stacks 2 is a multiple of the number of GTACs. This means that several fuel cell stacks 2 are connected via a second-order secondary air supply path 4.2 to a first-order secondary air supply path 4.1, each of which contains a GTAC. These are each supplied with pre-compressed air via the main air supply path 3, in which the air compressor unit 12 of the first compression stage 5.1 is arranged.

[0021] A further development of the system of Fig. 3 represents the system of Fig. 4. Here, to increase redundancy, the first compression stage 5.1 comprises two air compressor units 12, each of which is connected upstream of an air compressor unit 6 of the second compression stage 5.2 in a first-order secondary air supply path 4.1. The first-order secondary air supply paths 4.1 branch into second-order secondary air supply paths 4.2, via which the fuel cell stacks 2 are connected.

[0022] The Fig. 6 shows an example of implementation of the Fig. 1 represents the air system 1 shown.

[0023] The air compressor unit 12 of the first compression stage 5.1 is integrated into the main supply air path 3. It is designed as a multi-flow system and has a bypass path 14 with an integrated bypass valve 15 for bypassing the air compressor unit 12. It is driven by an electric motor 13. Downstream of the air compressor unit 12, the main supply air path 3 branches into four secondary supply air paths 4, each of which contains an air compressor unit 6 to form a second compression stage 5.2. The air compressor units 6 each have only one turbine 8 as their drive, which is integrated into an exhaust air path 7. Furthermore, a combustion chamber 9 is connected upstream of each turbine 8 and is connected to an anode subsystem 10 via a connecting line 11. Hydrogen can be supplied to the combustion chambers 9 via the connecting lines 11, and is oxidized in the combustion chambers 9. The air compressor units 6 of the second compression stage 5.2 are therefore designed as GTACs.

[0024] Cooling devices 17 are integrated into the respective secondary supply air path 4 upstream and downstream of the air compressor units 6. These are designed as gas-to-gas heat exchangers, with the air in the secondary supply air path 4 being tempered against the exhaust air in the exhaust air path 7. In the process, the air or exhaust air in the exhaust air path 7 is heated, so that already heated air or exhaust air is supplied to the combustion chambers 9. Furthermore, a stack bypass 14 is provided for bypassing the respective fuel cell stack 2.

[0025] The Fig.Figure 5 shows various possibilities for connecting a combustion chamber 9 to an anode subsystem 10. The anode subsystem 10 comprises an anode circuit 21, via which hydrogen from a hydrogen tank 24 and recirculated anode gas are supplied to the fuel cell stack 2. In this case, recirculation is achieved passively with the aid of a jet pump 22 and actively with the aid of a blower 23. The connecting line 11, which connects the combustion chamber 9 to the anode subsystem 10, can, for example, be a purge and / or drain line branching off from the anode circuit 21, in which a purge and / or drain valve 28 is arranged. The purge and / or drain valve 27 is opened at specific time intervals to remove nitrogen- and / or water-enriched anode gas from the anode circuit 21. According to a first variant, the connecting line 11 (see reference numerals in brackets) can also be connected to the hydrogen tank 24 orThe high-pressure volume connected to the hydrogen tank 24 can be connected upstream of a pressure control valve 25. A second variant provides for the connection to a medium-pressure volume downstream of the pressure control valve 25.

[0026] The following advantageous developments of the invention are explicitly referred to: An air system 1 according to the invention, wherein the first compression stage 5.1 comprises at least one air compressor unit 12 which is arranged in the main supply air path 3 or in a secondary supply air path 4.1 and has at least one electric motor 13 as a drive.

[0027] An air system 1 according to the invention, wherein the at least one air compressor unit 12 of the first compression stage 5.1 is arranged together with an air compressor unit 6 of the second compression stage 5.2 in a secondary supply air path 4.1.

[0028] An air system 1 according to the invention, wherein the at least one air compressor unit 12 of the first compression stage 5.1 is arranged in a first-order secondary supply air path 4.1, which branches into at least two second-order secondary supply air paths 4.2, in each of which an air compressor unit 6 of the second compression stage 5.2 is arranged.

[0029] A fuel cell system 20 with a plurality of fuel cell stacks 2, an air system 1 according to one of the preceding advantageous developments for supplying air to the fuel cell stacks 2 and at least one anode subsystem 10 for supplying the fuel cell stacks 2 with hydrogen.

Claims

[1] Air system (1) for supplying several fuel cell stacks (2) with air, comprising - a main supply air path (3) which branches into several secondary supply air paths (4.1, 4.2), and - an air compression system (5) with a first compression stage (5.1) and a second compression stage (5.2), wherein the second compression stage (5.2) comprises a plurality of air compressor units (6), each of which is arranged in a secondary supply air path (4.1, 4.2) and is coupled to a turbine (8) arranged in an exhaust air path (7) as the sole drive, wherein a combustion chamber (9) for the oxidation of hydrogen is integrated in each of the exhaust air paths (7) upstream of the turbines (8), which can be fed to the combustion chambers (9) via a connecting line (11) connected to an anode subsystem (10).

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