Fuel cell system for converting energy

Abstract

The invention relates to a fuel cell system (100) for converting energy. The fuel cell system (100) comprises: - a fuel cell stack (101), - an air inlet (103), - an exhaust pipe (105), - an air delivery system (107), - an additional compressor impeller (111) coupled to an electric machine (109), - a computing unit (113).

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] The ambient air is fed to a fuel cell stack via an air conveying system. This requires a correspondingly variable air mass flow and a corresponding pressure level.

[0004] The compression of the ambient air is often achieved using a thermal fluid machine. Optionally, energy recovery from the outflowing moist air can be achieved through recuperation using a turbine. Disclosure of the invention

[0005] 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.

[0006] The invention presented serves in particular to provide a robust and energy-efficient fuel cell system.

[0007] Thus, according to a first aspect of the invention presented, a fuel cell system for converting energy is presented.

[0008] The presented fuel cell system comprises a fuel cell stack, an air inlet, an exhaust line, an air conveying system, an auxiliary compressor impeller coupled to an electric machine, and a computing unit, wherein a main compressor impeller of the air conveying system is arranged in a first air guide path between a cathode inlet of the fuel cell stack and the air inlet, wherein the auxiliary compressor impeller is arranged in a second air guide path between a cathode outlet of the fuel cell stack and the exhaust line, wherein the auxiliary compressor impeller is coupled to an electric machine, and wherein the computing unit is configured to operate the electric machine coupled to the auxiliary compressor impeller in normal operation, in recirculation operation, or in emergency operation, wherein in normal operation the electric machine acts as a generator,to recuperate energy provided by a movement of the auxiliary compressor impeller, wherein in the recirculation mode the electric machine acts as a motor to circulate a gas volume enclosed in a volume closed to the environment by a movement of the auxiliary compressor impeller, and wherein in the emergency mode the electric machine acts as a motor to direct fresh air into the fuel cell stack.

[0009] In the context of the invention presented, a compressor impeller or auxiliary 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.

[0010] The presented invention is based on an additional compressor impeller, which is provided in addition to a main compressor impeller of an air conveying system of the presented fuel cell system.

[0011] The auxiliary compressor impeller is coupled, in particular reversibly coupled, to an electric machine, in particular a drive of the air conveying system of the fuel cell system.

[0012] Due to the location of the auxiliary compressor impeller between the cathode outlet of the fuel cell stack and the exhaust line, the auxiliary compressor impeller can perform various tasks and, for example, be driven in recuperation mode by air flowing out of the cathode outlet and, as a result, operate the electric machine as a generator and recuperate energy provided by the air conveying system into an energy storage device.

[0013] As an alternative to recuperation mode, the auxiliary compressor impeller can be actively driven. For this purpose, the auxiliary compressor impeller can be connected to a drive additional to a motor of the air handling system or use the motor of the air handling system.

[0014] By actively driving the auxiliary compressor impeller, it can be moved, for example, against the flow direction of an air mass flow flowing from the cathode outlet, so that, for example, air can be directed into the cathode outlet or air can be directed into a recirculation path.

[0015] The presented fuel cell system enables the following functions: - Inerting, oxygen depletion of the cathode path of the fuel cell stack, - homogenization of the fuel cell stack between cathode and anode, and - To enable redundancy or increased reliability of the fuel cell system in order to use this to advantage, in particular to improve the degradation of the fuel cell stack and increase its service life. Furthermore, a functional improvement in system behavior and an optimization of the operating strategy are achieved.

[0016] In recirculation mode, a gas volume sealed off from the environment can initially be generated in the air path or cathode subsystem of the fuel cell stack using appropriate valves.

[0017] The enclosed gas volume is circulated by the auxiliary compressor impeller and guided through the fuel cell stack, allowing oxygen to completely decompose from the gas volume in the fuel cell stack and inerting the cathode subsystem, primarily with nitrogen. For this purpose, the auxiliary compressor impeller can be operated in a direction opposite to normal operation as a blower or compressor wheel.

[0018] Recirculation operation requires only moderate speeds of the air conveying system, so that it is operated at partial load or in lower partial load mode.

[0019] Recirculation operation can be used for various operating modes outside of normal operation, such as shutting down / stopping the fuel cell system, bleed down of the fuel cell stack, or oxygen depletion and inerting in the closed cathode subsystem.

[0020] In standby mode, the fuel cell system draws no current / power from the fuel cell stack. However, the anode subsystem and cooling circuit usually continue to operate while the air supply to the fuel cell stack is shut off. In this state, recirculation mode can also be used to achieve or maintain inerting.

[0021] Start-stop operation is usually used in combination with standby mode. When starting the fuel cell system, recirculation mode can also be used to establish a defined initial state or homogenize the fuel cell stack.

[0022] Furthermore, highly damaging air-to-air starts, or OCV conditions, in which air / oxygen enters the anode subsystem and hydrogen is present in the anode subsystem without drawing current, can be avoided by inerting air into the cathode subsystem through the auxiliary compressor impeller. Accordingly, service life can be significantly increased.

[0023] During standstill phases of a vehicle comprising the fuel cell system, the recirculation mode can be activated from time to time, for example via a so-called “wake-up”, in order to maintain inerting even during the standstill period of the fuel cell system or the vehicle.

[0024] During normal operation, the auxiliary compressor impeller serves to recover energy. The recovered energy can be used, for example, to drive the air conveying system.

[0025] The presented fuel cell system can be designed as a two-stage compressed system with a first system for energy recuperation and a second system for high system pressures up to 6 bar.

[0026] The additional compressor impeller can also be designed as a double-flow variant, i.e. with a single-stage compression, but with a mass flow distribution between two impellers, which has advantages for the dynamics due to a lower moment of inertia as well as advantages for the axial force due to less bearing wear.

[0027] In the event of a fault, for example in the air supply system, the emergency operation allows the auxiliary compressor impeller to rotate in the opposite direction to normal operation in order to supply the fuel cell stack with air.

[0028] It may further be provided that the auxiliary compressor impeller is coupled to the electric machine via a magnetic coupling.

[0029] A magnetic coupling allows for different speeds to be achieved between the main compressor impeller of the air handling system and the auxiliary compressor impeller, especially when both compressor impellers are coupled to a single drive. This is advantageous for optimizing normal operation for efficiency.

[0030] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described 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.

[0031] They show: Fig. 1 a schematic representation of a possible design of the presented fuel cell system.

[0032] In Fig.1 shows a fuel cell system 100 for converting energy.

[0033] The fuel cell system 100 comprises a fuel cell stack 101, an air inlet 103, an exhaust line 105, an air conveying system 107, an auxiliary compressor impeller 111 coupled to an electric machine 109, and a computing unit 113.

[0034] A main compressor impeller 115 of the air conveying system 107 is arranged in a first air guide path 117 between a cathode inlet 119 of the fuel cell stack 101 and the air inlet 103.

[0035] The auxiliary compressor impeller 111 is arranged in a second air guide path 121 between a cathode outlet 123 of the fuel cell stack 101 and the exhaust line 105 and is coupled to the electric machine 109.

[0036] The computing unit 113 is configured to operate the electric machine 109 in a normal mode, as indicated by arrows opN 127, in a recirculation mode, as indicated by arrows opZ 129, or in an emergency mode, as indicated by arrows opF 131.

[0037] In normal operation, the electric machine 109 acts as a generator to recuperate energy provided by a movement of the auxiliary compressor impeller 111.

[0038] In the recirculation mode, the electric machine 109 acts as a motor to circulate a gas volume enclosed in a volume closed to the environment by a movement of the auxiliary compressor impeller 111.

[0039] In emergency operation, the electric machine 109 serves as a motor to supply fresh air to the fuel cell stack 101.

[0040] An optional passive gas-gas heat exchanger 133 transfers the heat from the supply air to the extract air.

[0041] An optional active gas coolant heat exchanger 135 removes the remaining heat required for component protection of the fuel cell stack.

[0042] In the illustrated embodiment, the auxiliary compressor impeller 111 can be decoupled from the electric machine 109 by means of a magnetic coupling 137, so that the electric machine 109 is only coupled to the main compressor impeller 115. This eliminates the need for an optional additional drive for the auxiliary compressor impeller 111.

[0043] A fuel cell stack bypass is introduced into the exhaust line 105 upstream of a valve 139, past both the fuel cell stack and the main compressor impeller 115.

[0044] The valves 139 and 141 are arranged in the supply air path upstream of a branch for the fuel cell stack bypass and in the exhaust air path downstream of the merging of the cathode exhaust air of the fuel cell stack 101 and the air mass flow via the fuel cell stack bypass.

[0045] The valves 139 and 141 make it possible to create a closed volume by allowing recirculation of cathode air via the additional compressor impeller 111.

[0046] The valve 139 can preferably be combined with a control valve 143, so that a throttle valve / valve is omitted.

[0047] The air is compressed in a single stage by the main compressor impeller 115.

[0048] During normal operation, the air is directed over the fuel cell stack 101. To maintain the pumping limit of the air delivery system 107, it may be necessary to divert a partial mass flow via the fuel cell stack bypass.

Claims

[1] Fuel cell system (100) for converting energy, the fuel cell system (100) comprising: - a fuel cell stack (101), - an air inlet (103), - an exhaust pipe (105), - an air delivery system (107), - an additional compressor impeller (111) coupled to an electric machine (109), - a computing unit (113), wherein a main compressor impeller (115) of the air conveying system (107) is arranged in a first air guide path (117) between a cathode inlet (119) of the fuel cell stack (101) and the air inlet (103), wherein the auxiliary compressor impeller (111) is arranged in a second air guide path (121) between a cathode outlet (123) of the fuel cell stack (101) and the exhaust line (105), wherein the auxiliary compressor impeller (111) is coupled to an electric machine (109), wherein the computing unit (113) is configured to to operate the electrical machine (109) coupled to the auxiliary compressor impeller (111) in normal operation, in recirculation operation or in emergency operation, wherein in normal operation the electric machine (109) acts as a generator to recuperate energy provided by a movement of the auxiliary compressor impeller (111), wherein in the recirculation mode, the electric machine (109) acts as a motor to circulate a gas volume enclosed in a volume closed to the environment by a movement of the auxiliary compressor impeller (111), wherein in emergency operation the electric machine (109) acts as a motor to supply fresh air into the fuel cell stack (101). [2] Fuel cell system (100) according to claim 1, characterized bythat the auxiliary compressor impeller (111) is coupled to the electric machine (109) via a magnetic coupling (137).

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