Fuel cell system for converting energy

Abstract

The presented invention relates to a fuel cell system (100) for converting energy, wherein the fuel cell system (100) comprises: - a fuel cell stack (101) comprising a cathode subsystem (103) and an anode subsystem (105), - an air delivery system (107), wherein the air conveying system (107) comprises a first compressor impeller (109) and a second compressor impeller (111), wherein the first compressor impeller (109) is fluidly coupled to a first air guide path (113), wherein the second compressor impeller (111) is fluidly coupled to a second air guide path (115), wherein the first air guide path (113) is configured to direct a first mass air flow from the first compressor impeller (109) into the cathode subsystem (103), wherein the second air duct path (115) is configured to direct a second mass air flow from the second compressor impeller (111) to the fuel cell stack (101) to cool it, and wherein the first compressor impeller (109) and the second compressor impeller (111) are connected to a drive (121) via a single common drive shaft (119).

Description

[0001] The presented invention relates to a fuel cell system according to the appended claims. State of the art

[0002] In fuel cell systems, the oxidizing agent oxygen from the ambient air and hydrogen as a reducing agent or fuel are usually used to react in the respective fuel cells to form water or water vapor and thus provide electrical power through electrochemical conversion.

[0003] It is known to use three media systems to supply a fuel cell stack, namely an air system for conveying and compressing air for a cathode subsystem, a hydrogen system with a tank for storing and dosing or recirculating hydrogen and a thermal system with coolant to dissipate the waste heat to the environment. Disclosure of the invention

[0004] The present invention proposes a drying method for drying a fuel cell stack. Further features and details of the invention are set forth in the respective subclaims, the description, and the drawings.

[0005] The invention presented serves in particular to provide a compact and cost-efficient fuel cell system.

[0006] Thus, according to a first aspect of the invention presented, a fuel cell system for converting energy is presented.

[0007] The presented fuel cell system comprises a fuel cell stack, a cathode subsystem, an anode subsystem and an air conveying system, wherein the air conveying system comprises a first compressor impeller and a second compressor impeller, wherein the first compressor impeller is fluidly coupled to a first air guide path, wherein the second compressor impeller is fluidly coupled to a second air guide path, wherein the first air guide path is configured to guide a first air mass flow from the first compressor impeller into the cathode subsystem, wherein the second air guide path is configured to guide a second air mass flow from the second compressor impeller to the fuel cell stack in order to cool the latter, and wherein the first compressor impeller and the second compressor impeller are connected to a drive via a single common drive shaft.

[0008] In the context of the invention presented, a compressor impeller is understood to mean a device for conveying air, such as a turbine or a paddle wheel, in particular a radial compressor impeller or an axial compressor impeller.

[0009] The presented fuel cell system is based on the integration of the thermal system into the air system, so that the fuel cell stack or the fuel cell system is cooled or cooled by an air mass flow. Accordingly, the presented fuel cell system can be designed particularly compactly by eliminating the need for a coolant-based cooling system with corresponding components, such as a coolant pump, electronics, valves, coolers, deionizers, line monitoring, and the like. This makes it particularly suitable as an additional or backup system, such as a so-called "range extender" to increase the range of, for example, a primarily battery-powered vehicle.

[0010] Furthermore, the presented fuel cell system is particularly low-maintenance due to the elimination of the coolant-based cooling system.

[0011] It is provided that the air conveying system comprises a first compressor impeller and a second compressor impeller, so that a first air mass flow and a second air mass flow can be generated, which are used for different tasks, namely for supplying the fuel cell stack with reaction air for the chemical reaction with hydrogen and for cooling the fuel cell stack.

[0012] Since the first compressor impeller and the second compressor impeller are arranged on a common single drive shaft, they can be driven by a single drive, such as an electric motor, eliminating the need for a second drive and allowing the fuel cell system to be designed particularly compactly. For example, the first compressor impeller and the second compressor impeller can be mounted on the shaft by gas bearings, in particular by two radial bearings and one axial bearing, which enable energy-optimized and oil-free operation.

[0013] Due to its design, the fuel cell system only comprises power electronics, a drive, a control unit and a wiring harness for providing the first air mass flow and the second air mass flow.

[0014] It can be provided that the first air guide path comprises a first air guide means which is configured to discharge a first partial mass flow from the first air guide path, and / or the second air guide path comprises a second air guide means which is configured to discharge a second partial mass flow from the second air guide path, wherein the fuel cell system comprises a computing unit which is configured to control the first air guide means and / or the second air guide means in order to adjust the first partial mass flow and / or the second partial mass flow.

[0015] In the context of the invention presented, an air guiding means is understood to mean an element for guiding air, such as an actuator, a valve, a branched line geometry or a throttle valve.

[0016] The first partial mass flow and / or the second partial mass flow can be fed to a further component of the fuel cell system, such as for ventilating a tank or an anode subsystem or an exhaust system for diluting exhaust gas to be emitted, in particular so-called “purge gas”, ie anode gas flushed out during a flushing process.

[0017] The first air guide path and the second air guide path can each contain an air filter. Preferably, a filter can also be used that is supplied with air through a central line and guides air into a first line to the first compressor impeller and into a second line to the second compressor impeller.

[0018] The first air guide path may optionally include a control valve.

[0019] Ventilation paths can be branched off from the first air guide path and / or the second air guide path, which can also serve as bypass paths.

[0020] The cooling air ducts in the fuel cell stack can be designed with a significantly smaller cross-section than a state-of-the-art coolant path. This allows the fuel cell stack to be designed particularly compactly.

[0021] To control the drive of the air conveying system, requirements of the cathode subsystem, thermal management of the fuel cell stack, respective ventilation elements and a purge / drain requirement are taken into account.

[0022] In addition, component-specific limits / requirements are taken into account, such as a surge limit, a minimum speed for any gas bearings used, a maximum speed and a stuffing limit of the air conveying system.

[0023] Requested by the cathode path, an air mass flow for the reaction in the fuel cell stack is determined by water management calculations or specifications including excess air lambda “mAirCath_Req”.

[0024] If a turbomachine is implemented, the surge limit must also be considered, so that at the requested pressure ratio "piAirCath_Req," a minimum required mass flow "mAirCathmin" is determined based on the surge limit. If this is greater than mAirCathmin > mAirCath_Req, then: mAirbypCath_Req=mAirCathmin−mAirCath_Req mAirCathmin<=mAirCath_Req then follows:mAirCath_Req=0

[0025] This would result in funding from CompAir4Cath: mAir_CompAir4Cath_Req=mAirCath_Req+mAirBypCath_Req

[0026] The calculation for the method is presented here as an example. However, it can be adapted to the individual topology of a particular fuel cell system.

[0027] If, for example, air bearings require additional cooling air mAirBearingsCath_Req and this would be taken from the cathode supply air path on the pressure side to or at the outlet of CompAir4Cath, the following would result: mAir_compAir4Cath_Req=mAirCath_Req=mAirCath_Req+mAirBypCath_Req+mAirBearingsCath_Req

[0028] The mass flow for heat removal from the fuel cell stack, "mAirCool_Req," is requested from the cooling air path. This can be determined analogously to the calculations described above, so that: mAir_CompAir4Cool_Req=mAirCool_Req+mAirBypCool_Req+mAirBearingsCool_Req

[0029] From the mass flow and pressure requirements: mAir_CompAir4Cath_Req,pAirCath_req→nminCath mAir_CompAir4Cath_Req,pAirCath_req→nminCool results in minimum required speeds, which results in a minimum required speed for the shaft to cover both requirements, with nWShaftmin = max(nminCath, nminCool)

[0030] This also results in the mass flows that are surplus in a path and can be used for other purposes, for the ventilation paths.

[0031] From nWShaftmin the set mass flows for each path and also the bypass mass flows (actual values) result.

[0032] If mAirBypCath_Ist >0 or mAirBypCool>0, then the respective excess mass flow can also be used for the ventilation systems branching off from this path.

[0033] If the individual ventilation paths are not coupled, the following 4 cases arise: F1: mAirVentCath_Req <= mAirBypCath_Ist excess sufficient F2: mAirVentCath_Req > mAirBypCath_Ist excess is not sufficient F3: mAirVentCool_Req <= mAirBypCool_Is excess sufficient F4: mAirVentCool_Req > mAirBypCool_Ist surplus is not sufficient

[0034] In cases F2, F4 where the surplus is not sufficient for the target ventilation mass flow, the difference dmAirVentCath=mAirVentCath_Req−mAirBypCath_Ist dmAirVentCool=mAirVentCath_Req−mAirBypCath_Ist by increasing the speed and increasing the mass flow. nWShaft_Req1>nWShaftmin

[0035] If the ventilation paths are coupled or if the same ventilation paths can be supplied from both the cathode path and the cooling air path, the calculation must be adjusted accordingly.

[0036] As an alternative to continuous ventilation, ventilation can also be carried out periodically or with a desired average mass flow mAirVent_Mean_Req.

[0037] This means that the mass flow requirement mAirVentCath_Req or mAirVentCool_Req does not have to be met precisely in time.

[0038] By averaging or integration, ventilation can also be adequately performed "on average." A time threshold can also be used, allowing a certain period of time with no or reduced ventilation. Only if the requirement is not met for too long can an increase in speed be enforced. These options can minimize additional energy consumption for ventilation.

[0039] The anode circuit must be periodically drained and purged to reduce nitrogen levels. This process also removes or purges hydrogen from the anode circuit. For explosion protection reasons, this hydrogen-containing gas mixture must be diluted with air to a level that ensures the explosion limit is not reached.

[0040] In order to enable this purge or purge / drain process, a sufficiently high air mass flow mAirDilutePurge_Req must be present at an inlet point into an air path.

[0041] The air for dilution at the inlet point can come from the cathode path or the first air guide path and / or the cooling air path or the second air guide path.

[0042] Where: mAirE > mAirDilutePurge_Req In cases where this is not met, the difference dmAirE=mAirDilutePurge_Req−mAirE by increasing the speed and increasing the mass flow, so that: nWShaft_Req2 > nWShaftmin.

[0043] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0044] They show: Fig. 1 a schematic representation of a possible design of the presented fuel cell system.

[0045] In Fig. 1 shows a fuel cell system 100 for converting energy.

[0046] The fuel cell system 100 includes a fuel cell stack 101, which includes a cathode subsystem 103 and an anode subsystem 105.

[0047] Furthermore, the fuel cell system 100 comprises an air conveying system 107, which comprises a first compressor impeller 109 and a second compressor impeller 111.

[0048] The first compressor impeller 109 is fluidly coupled to a first air guide path 113.

[0049] The second compressor impeller 111 is fluidly coupled to a second air guide path 115.

[0050] The first air guide path 113 is configured to guide a first air mass flow from the first compressor impeller 109 into the cathode subsystem 103 and the second air guide path 115 is configured to guide a second air mass flow along or through the fuel cell stack 101 through a cooling air path 117 in order to cool the fuel cell stack 101.

[0051] The first compressor impeller 109 and the second compressor impeller 111 are connected to a drive 121 via a single common drive shaft 119.

[0052] Via an air guide means 123 in the form of a 3-way valve, a partial mass flow can be branched off from an air mass flow flowing through the second air guide path 115 in order to ventilate a tank system, for example.

[0053] An exhaust path 125 serves as a collecting line for discharging exhaust gas emitted by the fuel cell system.

[0054] A computing unit 127 sets an air mass flow to the cathode subsystem 103, for example via an air guide means 129 and a bypass valve 131.

[0055] Additional air guide means 133 and 135 can be used to branch off partial mass flows, for example for ventilating a tank.

[0056] An anode circuit 137 is used for metering fuel or for recirculating anode gas.

[0057] Air flowing from an intake tract 139 is filtered via a first air filter 141 and a second air filter 143.

Claims

[1] Fuel cell system (100) for converting energy, wherein the fuel cell system (100) comprises: - a fuel cell stack (101), - a cathode subsystem (103), - an anode subsystem (105), - an air delivery system (107), wherein the air conveying system (107) comprises a first compressor impeller (109) and a second compressor impeller (111), wherein the first compressor impeller (109) is fluidly coupled to a first air guide path (113), wherein the second compressor impeller (111) is fluidly coupled to a second air guide path (115), wherein the first air guide path (113) is configured to guide a first air mass flow from the first compressor impeller (109) into the cathode subsystem (103), wherein the second air guide path (115) is configured to guide a second air mass flow from the second compressor impeller (111) to the fuel cell stack (101) in order to cool it, and wherein the first compressor impeller (109) and the second compressor impeller (111) are connected to a drive (121) via a single common drive shaft (119). [2] Fuel cell system (100) according to claim 1, characterized by , that the first air guide path (113) comprises a first air guide means (123) which is configured to discharge a first partial mass flow from the first air guide path (113), and / or the second air guide path comprises a second air guide means (129) configured to discharge a second partial mass flow from the second air guide path (115), wherein the fuel cell system (100) comprises a computing unit (127) configured to control the first air guiding means (123) and / or the second air guiding means (129) in order to adjust the first partial mass flow and / or the second partial mass flow.

Images