Method for discharging water from a fuel cell system, fuel cell system

Abstract

A method for discharging water from a fuel cell system (100), wherein the fuel cell system (100) has at least one fuel cell stack (101), an air path (10) in fluid communication with a cathode (105) of the fuel cell stack (101), an exhaust line (12), and a fuel line (20) in fluid communication with an anode (103) of the fuel cell stack (101), wherein at least one controllable valve (46) is arranged in the air path (10) and / or the exhaust line (12). The at least one controllable valve (46) is controlled by a control unit (60) in order to generate pressure oscillations.

Description

[0001] The invention relates to a method for discharging water from a fuel cell system having the features of the preamble of patent claim 1. State of the art

[0002] Hydrogen-based fuel cell systems are considered the mobility concept of the future because they emit only water as exhaust gas and enable fast refueling times. Fuel cell systems require air and hydrogen for the chemical reaction within the cells. To provide the required amount of energy, the fuel cells arranged within a fuel cell system are interconnected to form so-called fuel cell stacks. The waste heat from the cells is dissipated via a cooling circuit and released into the environment. The hydrogen required to operate fuel cell systems is usually supplied to the systems from high-pressure tanks.

[0003] Document DE 10 2006 013 699 A1 describes a fuel cell system with a fuel cell and an actuator actuated by a control unit for removing residual gas from a fuel flow of the fuel cell. It is characterized in that the control unit includes a control and / or regulation system that takes the fuel concentration in the fuel flow into account. Disclosure of the invention

[0004] The inventive method for operating a fuel cell system with the features of the independent claim has the advantage that, in contrast to conventional drying methods, local drying in the components is avoided and only the liquid water leading to ice formation is removed. This has a positive effect on the service life of the components of the fuel cell system.

[0005] Furthermore, the method according to the invention also removes liquid water quantities that usually remain in some channels or other narrow areas. This way, frost damage can be avoided and restarting can be improved.

[0006] The method according to the invention generates successive pressure oscillations or pulses in the cathode path or at the critical components. These pressure oscillations or pulses briefly create an increased differential pressure across the components, which is not achieved during the usual, constant drying procedure.

[0007] Advantageous embodiments and further developments of the fuel cell system according to the invention are specified in the dependent claims.

[0008] It is advantageous if an air compressor and / or compressor arranged in the air path generates a constant mass flow, as this allows the pressure fluctuations to be precisely adjusted by controlling the controllable valves. This can advantageously be achieved by an air compressor and / or compressor arranged in the air path that is set to a constant speed.

[0009] The at least one controllable valve is advantageously controlled with a signal pattern, in particular with a rectangle or a sawtooth, since this is easy to implement.

[0010] The at least one controllable valve can advantageously be controlled between the fully open and fully closed positions, as this is easy to implement. Alternatively, the at least one controllable valve can be controlled between a first position and a second position, with the pressure difference across the controllable valve changing between the first and second positions. This is advantageous if the pressure difference between the fully open and closed positions is to be reduced.

[0011] It is advantageous if the controllable valve, in particular a controllable throttle valve, is arranged in the air line between an air compressor and a humidifier, since in this way moisture can be removed particularly from the humidifier and its surroundings.

[0012] Furthermore, it is advantageous if the controllable valve, in particular a controllable throttle valve, is arranged in the exhaust line between the cathode and a humidifier, since in this way moisture can be removed particularly from the humidifier and its surroundings.

[0013] It shows: Fig. 1 a schematic representation of a fuel cell system according to the invention according to a first embodiment.

[0014] In the Fig. 1 shows a schematic topology of a fuel cell system 100 according to a first embodiment of the invention, comprising at least one fuel cell stack 101. The at least one fuel cell system 100 comprises an air path 10, an exhaust line 12, and a fuel line 20. The at least one fuel cell stack 101 can be used for mobile applications with high power requirements, for example, in vehicles or trucks, or for stationary applications, for example, in generators.

[0015] The air path 10 serves as an air supply line and is fluidly connected to a cathode 105 of the fuel cell stack 101. Air from the environment is supplied to the cathode 105 via an inlet 16 via the air path 10. Components required for the operation of the fuel cell stack 101 are arranged in the air path 10. An air compressor 11 and / or compressor 11 is arranged in the air path 10, which compresses or draws in the air according to the respective operating conditions of the fuel cell stack 101. Downstream of the air compressor 11 and / or compressor 11 is a humidifier 15, which humidifies the air in the air path 10 to a higher relative humidity. The humidifier 15 is designed as a passive humidifier, so that moisture is transported from the exhaust line 12 into the air path 10.

[0016] Additional components, such as a filter and / or a heat exchanger, may be provided within the air path 10. Oxygen-containing air is supplied to the fuel cell stack 101 via the air path 10.

[0017] The exhaust line 12 serves to transport exhaust gas into the environment via an outlet 18. The exhaust gas comprises a gas mixture with air components from the air path 10 and water. The exhaust gas from the exhaust line 12 can also contain hydrogen (H2) because portions of the hydrogen from the fuel line 20 can diffuse through the membrane of the fuel cell stack 101. Furthermore, hydrogen and a gas mixture with nitrogen can enter the exhaust line 12 via the purge line 40.

[0018] An H2 sensor 45 can be arranged in the exhaust line 12 to measure the concentration of hydrogen in the exhaust gas, since too much hydrogen must not be released into the environment via the exhaust line 12. Furthermore, the formation of an explosive mixture must be avoided.

[0019] At least one controllable valve 46, in particular a throttle valve, is arranged in the air path 10 and / or the exhaust line 12.

[0020] These can be controllable valves 46 which, according to the prior art, are already arranged in the air path 10 or the exhaust line 12, such as the shut-off valve which is arranged as a controllable valve 46 in the air line between the humidifier 15 and the cathode 105.

[0021] However, further controllable valves 46 can also be arranged in the air path 10 and the exhaust line 12, which functionally only serve to generate pressure oscillations.

[0022] This can be a controllable valve 46, in particular a controllable throttle valve, which is arranged in the air line 10 between the air compressor 11 and the humidifier 15.

[0023] Alternatively, this can be a controllable valve 46, in particular a controllable throttle valve, which is arranged in the exhaust gas line 12 between the cathode 105 and a humidifier 15.

[0024] The components and the piping system responsible for supplying the cathode with air are called the cathode side.

[0025] The fuel cell system 100 may further comprise a cooling circuit which is designed to cool the fuel cell stack 101. The cooling circuit is in the Fig. 1 is not shown because it is not part of the invention.

[0026] A tank 21 and a shut-off valve 22 are located at the inlet of the fuel line 20. Further components can be arranged in the fuel line 20 to supply an anode 103 of the fuel cell stack 101 with fuel as required.

[0027] In order to always supply the fuel cell stack 101 with sufficient fuel, there is a need for a superstoichiometric dosage of fuel via the fuel line 20. The excess fuel, as well as certain amounts of water and nitrogen that diffuse through the cell membranes to the anode side, are returned to a recirculation circuit 50 and mixed with the metered fuel from the fuel line 20.

[0028] Various components, such as a jet pump 51 driven by the metered fuel or a blower 52, can be installed to drive the flow in the recirculation circuit 50. A combination of jet pump 51 and blower 52 is also possible.

[0029] Since the amount of water and nitrogen continues to increase over time, the recirculation circuit 50 must be flushed from time to time so that the performance of the fuel cell stack 101 does not decrease due to an excessively high nitrogen concentration in the fuel line 20.

[0030] A purge line 40 is arranged between the recirculation circuit 50 and an exhaust gas line 12 so that the gas mixture can flow from the recirculation circuit 50 into the exhaust gas line 12.

[0031] A purge valve 41 is arranged in the purge line 40, which can open and close the connection between the recirculation circuit 50 and the exhaust line 12. The purge valve 41 is usually opened for a short time, so that the gas mixture is directed into the exhaust line 12 via the purge line 40.

[0032] The components and piping system responsible for supplying the anode with fuel are called the anode side.

[0033] The at least one controllable valve 46 is controlled by means of a control unit 60 in such a way that pressure oscillations are generated in the air path 10 and / or the exhaust line and / or the components arranged therein.

[0034] In order to generate pressure oscillations, the at least one controllable valve 46 is controlled between a first position and a second position, wherein the pressure difference across the controllable valve 46 changes between the first and second positions.

[0035] The first position may correspond to a full opening of the valve or throttle and the second position may correspond to a full closing of the valve or throttle.

[0036] However, it is also possible that the first and second positions are positions in which the valve or throttle valve is only partially open or closed.

[0037] The at least one controllable valve 46 can be controlled with a signal pattern, in particular with a rectangle or a sawtooth, wherein the maximum and minimum values ​​correspond to the first and second positions of the controllable valve 46 or the throttle valve.

[0038] An air compressor 11 and / or compressor 11 arranged in the air path 10 generates a constant mass flow. This can be achieved by setting the air compressor 11 and / or compressor 11 arranged in the air path 10 to a constant speed. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2006 013 699 A1

[0003]

Claims

[1] Method for discharging water from a fuel cell system (100), wherein the fuel cell system (100) has at least one fuel cell stack (101), an air path (10) fluidly communicating with a cathode (105) of the fuel cell stack (101), an exhaust line (12), a fuel line (20) fluidly communicating with an anode (103) of the fuel cell stack (101), wherein at least one controllable valve (46), in particular a throttle valve, is arranged in the air path (10) and / or the exhaust line (12), characterized by that the at least one controllable valve (46) is controlled by means of a control unit (60) in order to generate pressure oscillations. [2] Method according to claim 1, characterized by that an air compressor (11) and / or compressor (11) arranged in the air path (10) generates a constant mass flow. [3] Method according to claim 1, characterized bythat an air compressor (11) and / or compressor (11) arranged in the air path (10) is set to a constant speed. [4] Method according to claim 1, characterized by that the at least one controllable valve (46) is controlled with a signal pattern, in particular with a rectangle or a sawtooth. [5] Method according to claim 1, characterized by that the at least one controllable valve (46) is controlled between the positions fully open or fully closed. [6] Method according to claim 1, characterized by that the at least one controllable valve (46) is controlled between a first position and a second position, wherein the pressure difference across the controllable valve (46) changes between the first and second positions. [7] Fuel cell system (100) with at least one fuel cell stack (101), with an air path (10) in fluid communication with a cathode (105) of the fuel cell stack (101), with an exhaust line (12), with a fuel line (20) in fluid communication with an anode (103) of the fuel cell stack (101), wherein at least one controllable valve (46) is arranged in the air path (10) and / or the exhaust line (12), wherein the fuel cell system (200) is designed to carry out a method according to one of the preceding claims. [8] Fuel cell system (100) according to claim 7, characterized by that the controllable valve (46), in particular a controllable throttle valve, is arranged in the air line (10) between an air compressor (11) and a humidifier (15). [9] Fuel cell system (100) according to claim 7, characterized bythat the controllable valve (46), in particular a controllable throttle valve, is arranged in the exhaust gas line (12) between the cathode (105) and a humidifier (15).

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