WO2016124575A1

WO2016124575A1 - Fuel cell system and method for operating a fuel cell system

Info

Publication number: WO2016124575A1
Application number: PCT/EP2016/052152
Authority: WO
Inventors: Daniel Grundei; Oliver Kleppa
Original assignee: Volkswagen Ag
Priority date: 2015-02-05
Filing date: 2016-02-02
Publication date: 2016-08-11
Also published as: DE102015202088A1

Abstract

The invention relates to a fuel cell system having at least one fuel cell stack with cathode spaces and at least one cathode gas supply, comprising a cathode gas supply pathway for supply of a cathode operating gas to the cathode spaces and at least one first compressor disposed in the cathode gas supply pathway. It is envisaged that the fuel cell system has at least one second compressor, the second compressor having an electrical drive, and taking the form of a parallel circuit together with the first compressor.

Description

description

Fuel cell system and method for operating such

The invention relates to a fuel cell system having at least one fuel cell stack with cathode chambers and at least one cathode gas supply, the one

Cathode gas supply path for supplying a cathode operating gas into the

Includes cathode compartments. The invention further relates to a method for operating a

Fuel cell system comprising at least one fuel cell stack with cathode spaces and at least one cathode gas supply.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as core component the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a composite of an ion-conducting, in particular proton-conducting membrane and in each case an electrode arranged on both sides of the membrane (anode and cathode). During operation of the fuel cell, the fuel, in particular hydrogen H ₂ or a

Hydrogen-containing gas mixture, fed to the anode, where an electrochemical oxidation takes place with release of electrons (H ₂ -> 2 H ⁺ + 2 e ^" ). Via the membrane, which gas-tightly separates the reaction spaces and electrically isolated, takes place

(water-bound or anhydrous) transport of protons H ⁺ from the anode compartment into the cathode compartment. The electrons e ^" provided at the anode are fed to the cathode via an electrical line, and the cathode is supplied with oxygen or an oxygen-containing gas mixture, so that the oxygen is reduced by taking up the electrons (2 0 ₂ + 2 e -> 0 ^{2 ~} ). At the same time, these react in the cathode compartment

Oxygen anions with the protons transported across the membrane to form water (2 H ⁺ + O ^{2 "} -> H ₂ O).

In order to transport hydrogen or other process liquids, such as gases, coolants, ambient air or filtered air, use of compressors, for example turbochargers, in fuel cell systems is known.

DE 101 20 947 A1, DE 10 2004 051 359 A1 and DE 10 2010 035 727 A1 each describe fuel cell systems with a two-stage compression of the cathode gas. In particular, it is disclosed that the first compressor stage can be realized by an electromotive drive and the second stage by an exhaust-gas turbocharger, in which the one in the cathode gas supply line arranged compressor is coupled to a turbine disposed in the exhaust pipe.

In this case, according to DE 10 2010 035 727 A1, these stages can also be combined in a single machine. In addition, DE 10 2010 035 727 A1 describes a feed back of moist exhaust gas into the supply air of the fuel cell between the two compressor stages in order, inter alia, to achieve humidification.

DE 198 56 499 C1 describes a fuel cell system whose cathode operating gas is subjected to a two-stage compression, wherein a first compressor stage as

Exhaust gas turbocharger is formed, the compressor is thus driven via an exhaust gas driven by the cathode and / or anode exhaust gas, and the second compressor stage comprises an electric motor driven compressor. Between the two

Compressor stages, the cathode operating gas is humidified by water injection.

DE 10 201 1 1 15 846 A1 discloses in paragraph [0038] a fuel cell device comprising a turbocharger with a compressor having a first turbine and a second turbine. The script teaches in particular, as a compressor on two turbines

is to be driven to compress the charge pressure for the cathode operating gas of a fuel cell stack.

Also the control and regulation of compressors for the controlled supply of

Cathode operating gas in the direction of a fuel cell is known. For this purpose, WO 2010 / 020332A1 discloses, in particular, how a gas stream flows through a sensor device

Compressor is supplied. Furthermore, it shows, to measure the exhaust air flow of the compressor by means of a valve element. The knowledge of feed and discharge stream characterize the operating state of the compressor. His knowledge allows optimal control of supply and exhaust air flows of fuel cells.

DE 100 24 570 A1 shows the installation of two compressors on a common shaft. In this case, a compressor in the cathode gas supply path (Kathodenenzustromweg) and the second compressor in the cathode exhaust gas flow path are installed.

A disadvantage of the known prior art, in particular the sizes of existing fuel cell systems. Because these depend, among other things, on the sizes of built-in compressors. Compressors whose space is designed for use in fuel cell systems are not known. Existing compressors size the fuel cells due to their size. The oversizing of fuel cells increases their price and results in the loss of reaction times. The dynamic range of the fuel cell is disadvantageous. Because the compressors are not designed for use in fuel cells, they also do not run at the optimum operating point.

The invention is based on the object of proposing a fuel cell system which at least partially eliminates these disadvantages. These objects are also achieved in part or fully by a method of operating a fuel cell system having at least one fuel cell stack having the features of the independent claims.

In a fuel cell system with at least one fuel cell stack with

Cathode spaces and at least one cathode gas supply, comprising a

Cathode gas supply path for supplying a cathode operating gas into the

Cathode spaces and at least one disposed in the cathode gas supply path first compressor, this object is achieved in that the fuel cell system has at least a second compressor, the second compressor having an electric drive and is formed together with the first compressor as a parallel circuit.

Characterized in that the fuel cell system has at least a second compressor, wherein the second compressor has an electric drive and is formed as a parallel circuit together with the first compressor, the second compressor can be used as a so-called 'e-booster'. An 'e-booster' serves in particular as variable

Performance unit. The 'e-booster' can be advantageously switched on when the dynamic requirements of a start-stop operation of the fuel cell system quickly require a large change in the charge pressure of the cathode operating gas. Furthermore, the

, e-booster ', so the electrically driven compressor of small size, at high

Load requirements the first compressor switchable, so that the fuel cell stack, an increased boost pressure is provided. Because the 'e-booster' is designed small, its inert rotational masses are low. Because they are low, an e-Booster drive accelerates it quickly to a high RPM, quickly providing high boost pressure. The low inertial rotation masses of the 'e-Booster' thus increase its dynamic range compared to that of the first compressor. The first compressor can be made smaller by the combination with the 'e-booster'. Thus, weight and thus costs, especially when using fuel cell systems in vehicle construction, are reduced.

In a preferred embodiment, the second compressor is arranged in a bypass surrounding the first compressor. In a continuous operation can thus advantageously a Cathode operating gas can also be supplied bypassing the first compressor of the fuel cell.

Preferably, the inert rotational mass of the first compressor is greater than the sluggish

Rotational mass of the second compressor. This makes it possible to do the slow

Pressure build-up of the first compressor to compensate for the rapid pressure build-up of the second compressor.

In order to compensate for the slow adjustment of the boost pressure generated by the first compressor, the efficiency of the first compressor is advantageously lower than the efficiency of the second compressor.

In an advantageous embodiment, a conveyed mass flow of the first compressor is greater than the delivered mass flow of the second compressor. This allows the

Parallel connection of the two compressors are designed such that the second compressor is switched on or off at the optimum operating point of the first compressor. Thus, the first compressor, so the main compressor, always in an optimized lower

Running operating point. The main compressor can thus be designed for smaller loads and thus operates relatively more efficiently in operating areas of lower power.

In a preferred embodiment, the first compressor in a first power network and the second compressor in a second power network are arranged. This has in the

Vehicle area the advantage that the second compressor, for example, to the

Low-voltage network, for example, a 12V or a 48V network can be connected, while the first compressor can be powered by a high-voltage network.

The object is achieved in a further aspect of the invention by a method. The method of operating a fuel cell system solves the problem by switching at least a second compressor to increase the pressure of the cathode operating gas above ambient pressure. By such a method, in particular, the turbo lag of the first compressor can be bridged. In addition, the second compressor can be operated alone in the lower load range, if only small

Cathode operating gas mass flows are requested from the fuel cell stack.

In this case, at least one further method step can be carried out additionally or alternatively in any desired number and order. So the second compressor can be switched off when the first compressor reaches its operating performance. Further, the second compressor may be shut down to assist the run-up of the first compressor until it reaches its operating point.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with one another.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The invention is described below in embodiments with reference to the associated

Drawings explained. Show it:

FIG. 1 shows a schematic representation of a fuel cell system,

2 is a schematic representation of a fuel cell system with a first and second compressor in series,

3 shows a sectional view along the section line purple - purple or

lllb - lllb,

4 shows a fuel cell system with a first compressor and a second

Compressor in a parallel circuit,

Figure 5 is a schematic enlargement of the cathode gas supply path, and

Figure 6 is a schematic representation of a fuel cell system according to a preferred embodiment of the invention with a parallel connection of two second compressors with a first compressor.

FIG. 1 shows a fuel cell system 1, which is used, for example, in a vehicle, not shown. This vehicle is usually a

Electric vehicle (not shown) having an electric traction motor (not shown). This electric traction motor is supplied with electric power by the fuel cell system 1. The fuel cell system 1 comprises as a core component a fuel cell stack 2 which has a plurality of stacked individual cells. Each individual cell comprises in each case an anode space and a cathode space 3 which are separated from one another by an ion-conducting polymer electrolyte membrane (see detail section). The anode and cathode chamber 3 each comprise a catalytic electrode, the anode or the cathode (not shown), which catalyzes the respective partial reaction of the fuel cell reaction. Between two such membrane-electrode assemblies, an indicated bipolar plate is further arranged in each case, which serves to supply the operating media into the anode and cathode chambers 3 and also produces the electrical connection between the individual fuel cells.

To supply the fuel cell stack 2 with the operating gases, this has

Fuel cell system 1 on the one hand, an anode gas supply 34 and on the other hand, a cathode supply 4.

The cathode gas supply 4 comprises a cathode supply path 5, which supplies an oxygen-containing cathode operating gas 6 to the cathode compartments 3 of the fuel cell stack 2, in particular air which is drawn in from the environment. The

Cathode gas supply 4 further includes a cathode exhaust path 35 which connects the

Cathode exhaust gas (in particular the exhaust air) from the cathode compartments 3 of the

Fuel cell stack 2 dissipates.

To operate the fuel cell stack 2, it requires a cathode operating gas 6. The cathode operating gas 6 is fed along a cathode gas supply path 5

Fuel cell stack 2 supplied from a first compressor 7. This first compressor 7 is supplied either by a gas storage 25 with cathode operating gas 6 or is connected in the usual embodiment to the environment by means of a suction nozzle 26 and a filter 27. The first compressor 7 is in the example shown as electrical

powered turbocharger (ETL). The ETL supports the first compressor 7 connected to an electric motor 28. Thus, the first compressor 7 can be supplied with additional torque.

The first compressor 7 is according to the invention a second compressor 8 connected in parallel 10. To control a guided through the second compressor mass flow, which is

Parallel circuit 10 is provided with a valve 8a, the control of which allows feeding of cathode operating gas 6 in the parallel strand of the second compressor 8. The operation of the fuel cell system 1 is thus ensured by the cathode gas supply 4, 4a, 4b. The cathode gas supply 4 thus comprises inter alia the exhaust gas turbocharger 7 with turbine 16 and electric auxiliary drive 36 and a second small compressor 8 with valve 8b, the so-called 'e-booster', connected in parallel to this exhaust gas turbocharger with electric drive 28. The 'e-booster' is switched into the pressure build-up of the cathode gas supply path 5 when an increased cathode operating gas pressure is requested in the cathode compartments 3 of the fuel cell stack 2. The 'e-booster' is powered by its own electric drive 9, as well as the first compressor, the main compressor, here a turbocharger. For regulating the pressure or mass flow, a control element, for example a throttle flap 33, is located in the exhaust gas flow.

Fundamental goals of using turbochargers in fuel cell systems are regulation of the oxygen flow, for example as a function of the power consumption of a fuel cell. The regulated retrieval of power from the fuel cell is particularly important for the mobile use of fuel cells. An example of mobile use is an electromotive traction of vehicles. Among other things, turbochargers as

Exhaust gas turbocharger and electric turbocharger (ETL / ETC) known manner used. Exhaust gas turbochargers use a portion of an exhaust stream in a turbine to produce a torque. The torque is transmitted to support the drive or the drive of the turbocharger, so exhaust gas turbine and

Compressor together with an existing between them torque transmission form the exhaust gas turbocharger. Electrically driven turbochargers have an electric drive whose torque drives the turbocharger.

Electrically driven turbochargers allow more flexible boost pressure control. An adjustment of the optimal boost pressure at part load is given with them. The boost pressure depends, among other things, on the charge gas temperature and the compressor output. An electric drive of turbochargers is usually due to the sluggish rotational masses of turbochargers. The forces of an exhaust stream of fuel cells are usually not sufficient to accelerate the rotational masses quickly. Among the inert rotational masses of turbochargers or compressors include the masses of their blades and shafts. Also fasteners that connect blades and shafts together, can be counted to the inert rotational mass.

In order to supply a fuel cell stack with its operating media, ie the reactants, this one hand has an anode supply and on the other hand a Cathode supply on. The anode supply includes an anode supply path for supplying an anode operating gas into the anode spaces of the stack and a

Anode exhaust path for discharging an anode exhaust gas from the anode chambers, for example in the direction of an exhaust gas turbocharger.

FIG. 2 shows a fuel cell system 1 not belonging to the present invention in an embodiment with serial connection of the first compressor 7 and the second compressor 8. The serial connection of the second compressor 8 before the first compressor 7 compresses the cathode operating gas 6 or a second compressor

Operating medium 29, such as ambient air or oxidizing gases before. Thus, the pre-compressed cathode operating gas 6 from the first compressor can be compressed faster to operating pressure. Both the first compressor 7 and the second compressor 8 are bypassed by a bypass 1 1. The bypass 1 1 of the second compressor allows its bypass, so that only the first compressor can be supplied with cathode operating gas 6.

FIG. 3 shows a sectional view along the line of intersection purple - purple or IIIb - IIIb. The figure shows schematically a half section of a compressor 7 or a compressor 8.

Shown are the compressor shaft 30 and the blades 31st The compressor shaft 30 and the blades 31 are part of the inert rotational mass of the compressors 7, 8. The larger the inert rotational mass 13 of the first compressor 7, the more energy must be absorbed by the first compressor 7 in order to accelerate. The application of increased forces takes more time. This loss of time means a loss of dynamic for the first compressor 7. To compensate for this loss of momentum, the second compressor 8 can be added due to its lower inert rotational mass 14 in the pressure build-up of the cathode operating gas.

FIG. 4 shows a further schematic illustration of a fuel cell system 1. In the illustrated embodiment of a parallel connection of the first compressor 7 and the second compressor 8, a meaningful design form of both compressors can be seen. The compressors are expediently designed in such a way that a conveyed mass flow of the first compressor 17a, 17b (FIG. 5), for example of cathode operating gas 6, is greater than the delivered mass flow of the second compressor 18. By means of such a design, the first compressor can be considered electric supported turbocharger for setting or laying out the base load and the middle load range. Figure 6 shows a preferred embodiment of the fuel cell system with a

Parallel connection of the first compressor 7 and two second compressors 8. A multiple parallel connection of second compressors allows a precise compensation of the

Dynamic loss of the first compressor when it starts. In the present embodiment, the second compressor 8 is connected in parallel with the first second compressor 8 to compensate for its loss of dynamic at startup. In this embodiment, the first compressor 7 is connected in a first power grid 19. By contrast, the second compressor 8 is connected in a second power network 20. The second power grid is within one

Vehicle a low-voltage power system, such as the 12 V system or 48 V system. By separating the electrical supply of the first compressor 7 and second

Compressor 8, the power supply 32 of the electric drive of the first

Compressor 7 are designed to be smaller. This can be achieved at a power savings in the so-called turbo lag by means of the then switched on, e-Boosters' high operating pressures of the cathode operating gas 6. Consequently, there is a high

Cathode operating gas supply 6 for a heat exchanger 23 and a moisture exchanger 24 and thus a processed cathode operating gas 6 for the fuel cell 2 a. Also, the cathode gas pressures in the waste gate 22 are higher, so that an exhaust gas turbocharger can be driven faster. A compression is present in particular when the pressure of reactant liquids or gases is compressed above the ambient pressure 21.

By connecting several smaller compressors in parallel, the peak power can also be increased and a system can be easily scaled to several power classes.

Reference numeral list fuel cell system

fuel cell stack

cathode chambers

Cathode gas supply

a Cathode gas supply

b Cathode gas supply

Cathode gas supply path

Cathode operating gas

first compressor

second compressor

a valve

b second compressor with valve

electric drive

0 parallel connection

1 bypass

2 parallel connection of a bypass

3 inert rotational mass of the first compressor 4 inert rotational mass of the second compressor 5 efficiency of the first compressor

6 turbine

7 Efficiency of the second compressor

7a, b conveyed mass flow of the first compressor 8 funded mass flow of the second compressor 9 first power network

0 second power network

1 ambient pressure

2 waste gate

3 heat exchangers

4 humidity exchanger

5 gas storage

6 intake manifold

7 filters

8 electric motor

9 operating medium compressor shaft

blades

Power supply throttle

Anode gas supply cathode exhaust path electrical auxiliary drive

Claims

claims

1 . Fuel cell system (1) with at least one fuel cell stack (2) with

Cathode chambers (3) and at least one cathode gas supply (4, 4a, 4b), comprising a cathode gas supply path (5) for supplying a

Kathodenbetriebsgases (6) in the cathode compartments (3) and at least one in

Cathode gas supply path (5) arranged first compressor (7), characterized in that the fuel cell system (1) at least a second compressor (8), wherein the second compressor (8) has an electric drive (9) and together with the first compressor ( 7) is designed as a parallel connection (10).

2. Fuel cell system according to claim 1, characterized in that the second compressor (8) in a first compressor (7) circulating bypass (1 1) is arranged.

3. Fuel cell system according to claim 1 or 2, characterized in that the inert rotational masses (13) of the first compressor (7) are greater than the inert rotational masses (14) of the second compressor (8).

4. Fuel cell system according to one of the preceding claims, characterized

characterized in that the efficiency (15) of the first compressor (7) is less than the efficiency (16) of the second compressor (8).

5. Fuel cell system according to one of the preceding claims, characterized

in that a delivered mass flow (17) of the first compressor (7) is greater than the delivered mass flow (18) of the second compressor (8).

6. Fuel cell system according to one of the preceding claims, characterized

in that the first compressor (7) is arranged in a first power network (19).

7. Fuel cell system according to one of the preceding claims, characterized

in that the second compressor (8) is arranged in a second power network (22).

8. A method for operating a fuel cell system (1) according to one of claims 1 to 7, wherein the fuel cell stack (2) of the at least one in the

Cathode gas supply path (5) arranged first compressor (7) with

Cathode operating gas (6) is supplied and the at least one second compressor (8) is switched to the pressure of the cathode operating gas (6) via

Increase ambient pressure (21).

9. The method according to claim 8, characterized by the step that the second compressor (8) is switched off when the first compressor (7) reaches its operating performance.

10. The method according to claim 8 or 9, characterized by the step that the second compressor (8) is turned off when the first compressor (7) the

Cathode gas (6) compacted.