Method for operating an air system, air system and fuel cell system

Abstract

The invention relates to a method for operating an air system (1) for supplying at least one fuel cell stack (2) with air, comprising an air supply path (3) and an air conveying and air compression system (4) integrated into the air supply path (3) with several shaft-rotor units (5) connected in series, the shafts (6) of which are rotatably mounted via gas bearings (7, 8), further comprising an exhaust air path (9) for removing the air exiting the fuel cell stack (2) and at least one throttling device integrated into the exhaust air path (9), preferably in the form of a turbine (10) and / or a pressure regulating valve. According to the invention, the gas bearings (7, 8) are temperature-controlled with air, which - downstream of the last wave rotor unit (5) in the series from the supply air path (3) or - upstream of at least one throttling device from the exhaust air path (9) is branched off and supplied in reverse order to the gas bearings (7, 8) of the shaft-rotor units (5), so that first the gas bearings (7, 8) of the last shaft-rotor unit (5) in series and then the gas bearings (7, 8) of at least one further shaft-rotor unit (5) are tempered with the air. The invention further relates to an air system (1) and a fuel cell system (20) with an air system (1) according to the invention.

Description

[0001] The invention relates to a method for operating an air system having the features of the preamble of claim 1. The air system serves to supply at least one fuel cell stack of a fuel cell system with air. Furthermore, the invention relates to an air system for a fuel cell system having at least one fuel cell stack and to a fuel cell system having an air system according to the invention.

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

[0003] Fuel cells convert a fuel, such as hydrogen, and oxygen into electrical energy, heat, and water. The oxygen source is typically air, generally ambient air. The air supply is provided by an air system that includes an air supply path for supplying air and an exhaust path for removing the air exiting or exhausting the fuel cells.

[0004] Since the electrochemical reaction in the fuel cells requires a certain air mass flow and a certain pressure level, the air is first compressed. For this purpose, an air conveying and compression system is integrated into the supply air path. This system comprises at least one thermal turbomachine driven by an electric motor and / or a turbine to compress the air. The turbine has the advantage of recovering some of the energy used for compression (energy recuperation).

[0005] Higher system pressures generally require multi-stage compression of the air in the supply air path and energy recovery using a turbine. Multi-stage compression is achieved using air conveying and compression systems with two or more shafts. Each shaft houses at least one impeller of a compressor and / or turbine. The at least one impeller and the shaft together form a shaft-rotor unit.

[0006] The requirements regarding air mass flow and pressure result in high speeds for the thermal turbomachines. When using thermal turbomachines in a fuel cell system, the conveyed and compressed air must also be oil-free. This requires the shafts to be rotatably mounted via gas bearings. Typically, passive gas bearings are used, which create an air cushion through rotation, so that above a certain speed, only air friction is present.

[0007] A shaft-rotor unit of a thermal turbomachine typically has two radial bearings and one axial bearing. These must be actively tempered, specifically cooled, during operation of the thermal turbomachine, for example, with previously compressed air from the supply air path. The cooling air requirement is considerable and has consequences for the design of the entire system. The more cooling air is diverted from the supply air path, the less air is available to the at least one fuel cell stack, thus reducing the overall efficiency of the system. To meet the additional air demand, the air conveying and air compression system must be larger, which increases the energy requirement. This means that the at least one fuel cell stack must also be larger to provide the energy. As a result, hydrogen consumption increases.

[0008] If the air conveying and compression system has more than one shaft-rotor unit, the cooling air requirement increases dramatically, as air is diverted from the supply air path after each compression stage and supplied as cooling air to the gas bearings of the shaft-rotor unit of the respective compression stage. Multi-shaft air conveying and compression systems therefore have a systemic disadvantage associated with high costs and high hydrogen consumption.

[0009] The present invention is concerned with the task of eliminating the systemic disadvantage of multi-shaft air conveying and air compression systems in order to reduce costs and hydrogen consumption.

[0010] To achieve this objective, the method having the features of claim 1 and the air system having the features of claim 5 are proposed. Advantageous developments of the invention can be found in the respective subclaims. Furthermore, a fuel cell system with an air system according to the invention is specified. Disclosure of the invention

[0011] A method is proposed for operating an air system for supplying at least one fuel cell stack with air. The air system comprises an air supply path and an air conveying and air compression system integrated into the air supply path, comprising several series-connected shaft-rotor units whose shafts are rotatably mounted via gas bearings. The air system further comprises an exhaust air path for discharging the air escaping from the fuel cell stack, as well as at least one throttle device integrated into the exhaust air path, preferably in the form of a turbine and / or a pressure control valve. According to the invention, the gas bearings are tempered with air, which - downstream of the last shaft-rotor unit in the row from the supply air path or - upstream of the at least one throttle device, it is branched off from the exhaust air path and fed in reverse order to the gas bearings of the shaft-rotor units, so that first the gas bearings of the last shaft-rotor unit in the series and then the gas bearings of the at least one further shaft-rotor unit are tempered with the air.

[0012] In the proposed process, air is diverted only once from the supply air path or the exhaust air path and supplied sequentially as cooling air to the gas bearings of the shaft-rotor units. This means that the diverted cooling air is used multiple times, or the gas bearings of several shaft-rotor units are cooled with the same cooling air. This significantly reduces the cooling air requirement. This eliminates the systemic disadvantage of a multi-shaft air conveying and compression system.

[0013] According to the proposed method, the air required to control the temperature of the gas bearings is diverted from a pressurized area of ​​the air system, allowing the cooling air to be supplied to the gas bearings via an existing pressure gradient. Since the pressure level is highest in the supply air path downstream of the last shaft-rotor unit in the series and in the exhaust air path upstream of at least one throttle device, the cooling air is diverted there.

[0014] In a further development of the invention, it is proposed that the air diverted from the supply air path or the exhaust air path for temperature control of the gas bearings be cooled at least upstream of the gas bearings of the last shaft-rotor unit in the series. This means that the diverted cooling air is first cooled itself before being fed to a gas bearing for temperature control, in particular for cooling. This is advantageous because the air heats up during compression, so the proposed cooling of the air can improve the cooling effect.

[0015] Ideally, the air diverted to control the temperature of the gas bearings is cooled multiple times, for example, upstream of the gas bearings of a shaft-rotor unit. This allows for intermediate cooling of the air, ensuring effective cooling of the gas bearings of at least one additional shaft-rotor unit.

[0016] The air diverted to control the temperature of the gas storage can be cooled by a cooling device integrated into the supply air path and / or the exhaust air path. This can, for example, comprise a heat exchanger through which a coolant from a cooling circuit flows.

[0017] According to a preferred embodiment of the invention, the air diverted from the supply air path or the exhaust air path is guided through a coolant-cooled cooling jacket of the shaft-rotor unit, with the aid of which the air has previously been compressed. This eliminates the need for an additional cooling device, thus saving installation space. However, this requires that the shaft-rotor unit, preferably all shaft-rotor units, each have a coolant-cooled cooling jacket.

[0018] Furthermore, it is proposed that the air diverted from the supply air path or the exhaust air path for temperature control of the gas storage be discharged directly or indirectly via the exhaust air path to the environment downstream of the gas storage to be temperature controlled. The air used for temperature control is thus returned to a pressure level that at least approximately corresponds to the ambient pressure.

[0019] Furthermore, an air system for a fuel cell system with at least one fuel cell stack is proposed. The air system comprises: - an air supply path and an air conveying and air compression system integrated into the air supply path with several shaft-rotor units connected in series, the shafts of which are rotatably mounted via gas bearings, and - an exhaust air path and at least one throttle device integrated into the exhaust air path, preferably in the form of a turbine and / or a pressure control valve.

[0020] According to the invention, an air path for tempering the gas bearings of the series-connected shaft-rotor units branches off from the supply air path downstream of the last shaft-rotor unit in the series or from the exhaust air path upstream of the at least one throttle device, wherein the air path is guided in reverse order via the gas bearings of the last shaft-rotor unit in the series to the gas bearings of the at least one further shaft-rotor unit.

[0021] The proposed air system is particularly suitable for implementing the previously described process or can be operated according to this process, thus achieving the same advantages. In particular, the inherent systemic disadvantage of multi-shaft air conveying and air compression systems, which drives up costs and hydrogen consumption, can be eliminated.

[0022] Preferably, the air path for cooling the diverted air is routed through at least one cooling device, preferably through a coolant-cooled cooling jacket of a shaft-rotor unit. The diverted air, which has previously heated up during compression, can be cooled in this way before being fed to the gas bearings for temperature control, in particular for cooling. This increases the cooling effect of the diverted air. Ideally, each shaft-rotor unit has a coolant-cooled cooling jacket over which the air path is routed, so that intermediate cooling of the diverted air is achieved at the same time. Before the air is fed to the gas bearings of a shaft-rotor unit, it is first passed through the cooling jacket of the respective shaft-rotor unit and cooled thereby.

[0023] Furthermore, the gas bearings of the shaft-rotor units preferably each comprise at least one radial bearing and one axial bearing, through which the air path is guided. Preferably, the air path leads through two radial bearings and one axial bearing of a shaft-rotor unit.

[0024] Furthermore, it is proposed that the air path downstream of the gas storage units to be temperature-controlled be connected to the environment directly or indirectly via the exhaust air path. In this way, the diverted air can be returned to a pressure level that at least approximately corresponds to the ambient pressure. This means that a pressure gradient exists in the air path, via which the air diverted into the air path can be supplied to the gas storage units.

[0025] Advantageously, a controllable device, for example a valve, is integrated into the air path, with the aid of which the air mass flow in the air path can be controlled depending on the operating point.

[0026] Since the air system according to the invention is particularly suitable for use in a fuel cell system, a fuel cell system comprising at least one fuel cell stack and an air system according to the invention is also proposed. The air system can be used to supply the at least one fuel cell stack with air. The advantages of the air system according to the invention also extend to the fuel cell system. In particular, less air is required to control the temperature of the gas bearings of the multiple shaft-rotor units, so that neither the air conveying and air compression system nor the at least one fuel cell stack need to be designed larger. In this way, costs and hydrogen consumption can be reduced.

[0027] Preferred embodiments of the invention 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, Fig. 2 a schematic representation of a second air system according to the invention, 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 shaft-rotor unit of an air conveying and air compression system for an air system according to the invention, Fig. 6 a schematic representation of a shaft-rotor unit of an air conveying and air compression system for an air system according to the invention, Fig. 7 a schematic representation of a shaft-rotor unit of an air conveying and air compression system for an air system according to the invention, Fig. 8 a schematic representation of a shaft-rotor unit of an air conveying and air compression system for an air system according to the invention, Fig. 9 a schematic representation of a shaft-rotor unit of an air conveying and air compression system for an air system according to the invention and Fig. 10 a schematic representation of a shaft-rotor unit of an air conveying and air compression system for an air system according to the invention. Detailed description of the drawings

[0028] The Fig. Figure 1 shows, by way of example, a first preferred embodiment of an air system 1 according to the invention for supplying at least one fuel cell stack (not shown) with air. The air system 1 comprises an air supply path 3, into which a multi-stage and thus multi-shaft air conveying and compression system 4 for compressing the air is integrated. In the present case, the air conveying and compression system 4 comprises two series-connected shaft-rotor units 5, whose shafts 6 are supported by gas bearings 7, 8, namely two radial bearings 7 and one axial bearing 8 for each shaft 6. The shaft-rotor units 5 are each driven by an electric motor 19 and a turbine 10. The turbines 10 are integrated into an exhaust air path 9 of the air system 1, so that the air exiting the at least one fuel cell stack can be supplied to them. In this way, part of the energy used for compression can be recovered.Downstream of the last turbine 10, the air is discharged to the environment 11.

[0029] To cool the gas bearings 7, 8 of the two shaft-rotor units 5, an air path 12 is provided, which branches off from the supply air path 3 downstream of the last shaft-rotor unit 5 in the series. The air path 12 is initially routed via a cooling device 13, which can, for example, be a coolant-cooled cooling jacket of the shaft-rotor unit 5. The air path 12 is then routed via the gas bearings 7, 8 of the last shaft-rotor unit 5 in the series. From there, it goes to another cooling device 13, which can again be a coolant-cooled cooling jacket of the further shaft-rotor unit 5. Downstream of all gas bearings 7, 8, the air is discharged to the environment 11 directly via the air path 12 or indirectly via the exhaust air path 9. Since the air path branches off from the supply air path 3 in the printed area, there is a pressure gradient in the air path 12, which is used for air transport.The decreasing pressure gradient over the length of the air path 12 is indicated by the varying line thickness.

[0030] A second air system 1 according to the invention is the Fig. 2. Here, the air path 12 does not branch off from the supply air path 3, but from the exhaust air path 9, upstream of the turbines 10. Here, too, a pressure gradient prevails in the air path 12. However, the air branched off from the exhaust air path 9 may be humid, which may lead to restrictions and / or additional measures. For example, drying of the air path 12 may be necessary. For this purpose, dry air from the supply air path 3 can be introduced into the exhaust air path 9, bypassing the at least one fuel cell stack. Otherwise, the air system 1 can be identical to the air system 1 of the Fig. 1 be constructed.

[0031] Fig. Figure 3 shows a third air system 1 according to the invention, which serves to supply a single fuel cell stack 2 with air in a fuel cell system 20. As exemplified in the Fig. 3, the multi-stage and thus multi-shaft air conveying and air compression system 4 comprises a first shaft-rotor unit 5, which is driven by an electric motor 19, and a downstream second shaft-rotor unit 5, which is driven only by means of a turbine 10 integrated into the exhaust air path 9.

[0032] The air required by the fuel cell stack 2 is taken from the environment 11 and fed via an air filter 21 to the first shaft-rotor unit 5 for compression. Since the air heats up during compression, it is cooled or intercooled by a first cooling device 13 integrated into the supply air path 3. The air is then further compressed by the second shaft-rotor unit 5. With the help of at least one further cooling device 13 arranged downstream of the second shaft-rotor unit 5, the compressed air is cooled again before entering the fuel cell stack 2. The air exiting the fuel cell stack 2 is discharged back into the environment 11 via the exhaust air path 9, having first been fed to the turbine 10 integrated into the exhaust air path 9. If necessary, the turbine 10 can be bypassed via a turbine bypass 16 with an integrated bypass valve 17.Furthermore, a stack bypass 14 with an integrated bypass valve 15 is provided, which allows bypassing of the fuel cell stack 2. If the fuel cell stack 2 is to be completely separated from the air system 1, this can be achieved by closing two shut-off valves 18.

[0033] In the Fig. 3, the air path 12, via which air can be supplied to the gas bearings 7, 8 of the shaft-rotor units 5 for temperature control, branches off from the supply air path 3, so that compressed, dry air is supplied to the gas bearings 7, 8. The decreasing pressure gradient in the air path 12 is again indicated by the line thickness representing the air path 12. To cool the air branched off into the air path 12, the air can be passed through at least one cooling device 13, for example, through the cooling device 13 serving for intermediate cooling, which is arranged between the two shaft-rotor units 5 in the supply air path 3.

[0034] The Fig. 4 shows another fuel cell system 20. This system has two fuel cell stacks 3 and an air system 1 according to the invention for supplying the fuel cell stacks 2 with air. The air system 1 comprises an air conveying and compression system 4 with two shaft-rotor units 5, each of which is driven by an electric motor 19 and a turbine 10. A cooling device 13 is provided between the two shaft-rotor units 5 for intermediate cooling of the air in the supply air path 3.

[0035] The Fig. 1 to 4 clearly show that the topology of an air system 1 according to the invention can vary, particularly with regard to the design of the multi-stage or multi-shaft air conveying and air compression system 4 as well as with regard to other components. Fig. 5 to 10, various shaft-rotor units 5 are described below by way of example, which can be used in an air system 1 according to the invention to realize at least one compression stage.

[0036] Fig. Figure 5 shows a shaft-rotor unit 5 with an electric motor 19, so that the shaft 6 of the shaft-rotor unit 5 is driven purely by an electric motor. The gas bearings 7, 8 of the shaft 6 of the shaft-rotor unit 5 are in the Fig. 5 is not shown. The rotor-shaft unit 5 is already Fig. 3 known.

[0037] Fig. Figure 6 shows a shaft-rotor unit 5, which is driven by an electric motor 19 and a turbine 10. The turbine 10 is integrated into an exhaust air path 9. Examples are shown in the Fig. 6 shows the gas bearings 7, 8 for supporting the shaft 6. The rotor-shaft unit 5 of the Fig. 6 is already out of the Fig. 1, Fig. 2 and Fig. 4 known.

[0038] Fig. Figure 7 shows a multi-flow shaft-rotor unit 5, on whose shaft 6 two impellers 5.1, 5.2 of a compression stage are arranged. The shaft-rotor unit 5 is driven by an electric motor 19.

[0039] Fig. 8 shows a shaft-rotor unit 5 with a shaft 6, on which two impellers 5.1, 5.2 are also arranged, whereby the impellers 5.1, 5.2 - in contrast to Fig. 7 - are not parallel, but sequentially. This allows for intermediate cooling of the air, provided - as in the Fig. 8 - a cooling device 13 is integrated into the supply air path 3. The shaft-rotor unit 5 of the Fig. 8 is also driven by an electric motor 19.

[0040] Fig. 9 shows a shaft-rotor unit 5 which is driven solely by a turbine 10. The turbine 10 is integrated into an exhaust air path 9. Such a shaft-rotor unit 5 is already known from Fig. 3 known.

[0041] Fig. 10 shows a shaft-rotor unit 5 with a shaft 6 and two impellers 10.1, 10.2 arranged thereon, which are two turbine wheels for purely generator operation.

[0042] In an air conveying and air compression system 4 for an air system 1 according to the invention, several similar and / or different shaft-rotor units 5 can be used in combination.

Claims

[1] Method for operating an air system (1) for supplying at least one fuel cell stack (2) with air, comprising an air supply path (3) and an air conveying and air compression system (4) integrated into the air supply path (3) with a plurality of shaft-rotor units (5) connected in series, the shafts (6) of which are rotatably mounted via gas bearings (7, 8), further comprising an exhaust air path (9) for discharging the air emerging from the fuel cell stack (2) and at least one throttle device integrated into the exhaust air path (9), preferably in the form of a turbine (10) and / or a pressure control valve, characterized by that the gas bearings (7, 8) are tempered with air, the - downstream of the last shaft-rotor unit (5) in the row from the supply air path (3) or - branched off from the exhaust air path (9) upstream of the at least one throttle device and fed in reverse order to the gas bearings (7, 8) of the shaft-rotor units (5), so that first the gas bearings (7, 8) of the last shaft-rotor unit (5) in the series and then the gas bearings (7, 8) of the at least one further shaft-rotor unit (5) are tempered with the air. [2] Method according to claim 1, characterized by that the air branched off from the supply air path (3) or from the exhaust air path (9) for tempering the gas bearings (7, 8) is cooled at least upstream of the gas bearings (7, 8) of the last shaft-rotor unit (5) in the series. [3] Method according to claim 2, characterized by that the air branched off from the supply air path (3) or the exhaust air path (9) is guided for cooling through a coolant-cooled cooling jacket of the shaft-rotor unit (5), with the aid of which the air has previously been compressed. [4] Method according to one of the preceding claims, characterized by that the air branched off from the supply air path (3) or the exhaust air path (9) for tempering the gas bearings (7, 8) is discharged downstream of the gas bearings (7, 8) to be tempered directly or indirectly via the exhaust air path (9) to the environment (11). [5] Air system (1) for a fuel cell system (20) with at least one fuel cell stack (2), comprising - an air supply path (3) and an air conveying and air compression system (4) integrated into the air supply path (3) with several shaft-rotor units (5) connected in series, the shafts (6) of which are rotatably mounted via gas bearings (7, 8), and - an exhaust air path (9) and at least one throttle device integrated into the exhaust air path (9), preferably in the form of a turbine (10) and / or a pressure control valve, characterized byin that an air path (12) for tempering the gas bearings (7, 8) of the series-connected shaft-rotor units (5) branches off from the supply air path (3) downstream of the last shaft-rotor unit (5) in the series or from the exhaust air path (9) upstream of the at least one throttle device, wherein the air path (12) is guided in reverse order via the gas bearings (7, 8) of the last shaft-rotor unit (5) in the series to the gas bearings (7, 8) of the at least one further shaft-rotor unit (5). [6] Air system (1) according to claim 5, characterized by that the air path (12) for cooling the branched air is guided through at least one cooling device (13), preferably through a coolant-cooled cooling jacket of a shaft-rotor unit (5). [7] Air system (1) according to claim 5 or 6, characterized by that the gas bearings (7, 8) of the shaft-rotor units (5) each comprise at least one radial bearing (7) and one axial bearing (8) over which the air path (12) is guided. [8] Air system (1) according to one of claims 5 to 7, characterized by that the air path (12) downstream of the gas storage (7, 8) to be tempered is connected directly or indirectly via the exhaust air path (9) to the environment (11). [9] Air system (1) according to one of claims 5 to 8, characterized by that a controllable device, in particular a valve (22), is integrated into the air path (12), with the aid of which the air mass flow in the air path (12) can be controlled depending on the operating point. [10] Fuel cell system (20) with at least one fuel cell stack (2) and an air system (1) according to one of claims 5 to 9.

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