WO2015082304A1

WO2015082304A1 - Fuel cell apparatus with improved fuel circulation in the lower power range, and method for this

Info

Publication number: WO2015082304A1
Application number: PCT/EP2014/075813
Authority: WO
Inventors: Maik Kraus
Original assignee: Volkswagen Ag
Priority date: 2013-12-06
Filing date: 2014-11-27
Publication date: 2015-06-11
Also published as: DE102013225115A1

Abstract

The invention relates to an apparatus (10) comprising a storage apparatus (110) for compressed fuel; and comprising a fuel cell stack (100) having a circulation apparatus (130, 140, 150) for a fuel circuit, a line (170) for supplying air, and a further line (190) for discharging air, wherein a drive nozzle (200) is arranged in the circulation apparatus (130, 140, 150), said drive nozzle being connected to the storage apparatus (110) such that fuel which flows out of the storage apparatus (110) at least partially drives the circulation; comprising an air delivery apparatus (230) for providing a compressed air flow, which is required for supplying the fuel cell stack (100), to the line (170) for supplying air; and relates to a method for operating an apparatus of this kind. Provision is made for the circulation apparatus (130, 140, 150) to further comprise a turbine (210) which is coupled to a further turbine (220) which is connected to the air delivery apparatus (230) such that the circulation can be driven by means of an excess compressed air flow.

Description

description

FUEL CELL DEVICE WITH IMPROVED FUEL CIRCULATION IN LOWER

PERFORMANCE, AND METHOD THEREFOR

The present invention relates to a device with a fuel cell stack and a method for operating such a device.

Fuel cell stacks produce electrical energy through the reaction of fuel (eg, hydrogen) from a storage device or supply network with oxygen, such as ambient air. In this case, oxygen is supplied to the stack on one cathode side and fuel is supplied to the stack on an anode side.

Since the anode reaction is usually operated with overstoichiometric design of the fuel, there is no complete reaction of all the fuel supplied in the fuel cell stack. Nor does a complete reaction of the oxygen take place. For efficient use of the fuel it is therefore often recirculated

(Recirculated), so that before refilling the fuel to the fuel cell stack, the fuel is enriched again so far that again a stoichiometric measurement of the fuel is present and the reaction can take place.

If the fuel for enrichment under pressure, this can be used for example by means of a motive nozzle for enrichment, so that the motive nozzle also causes the circuit is driven and the remaining fuel is recirculated. An example of a fuel cell system with a motive nozzle is disclosed in EP 1421639 B1.

Another way to recirculate the remaining fuel is in the

Use of electric motor driven blower.

Finally, the use of turbines that are pressurized with pressurized gas is also described. This gas is used, which in the

Fuel cell system is incurred anyway. JP 08 203547 A acts on the turbine

for example, with the pressurized fuel. JP 2003 031244 A uses cathode exhaust gas for driving a turbine. Also in EP 1 630 180 A1 a means

Described cathode exhaust gas turbine for a fuel cell system. EP 2 176 91 1 B1 describes a drive turbine which is driven by compressed air of an air supply unit.

The inventors of the present invention have recognized that the efficiency of

Fuel cell stacks can be further increased.

The invention has for its object to provide a device with a storage device for compressed fuel and a fuel cell stack, which can be operated without or with less effort on parasitic energy and in such a way that in the fuel cell stack improved implementation of existing in the supplied fuel chemical energy can be done in electrical energy.

According to the invention therefore an apparatus according to claim 1 and a method according to claim 5 is proposed.

Although the present invention is based on the finding that the motive nozzle and turbine can each represent a circulatory drive without parasitic, ie without additional energy consumption, the fuel cells only in different ones

Supply power areas optimally with fuel.

The device proposed according to the invention comprises a compressed fuel storage device and a fuel cell stack with a circulation circuit for a fuel circuit, an air supply and an air discharge. It is in the

Circuit device arranged a driving nozzle, which is connected to the storage device, that fuel flowing out of the storage device at least partially drives the circuit. Furthermore, the device comprises an air conveying device for

Providing a compressed air flow to the supply of oxygen needed to supply the fuel cell stack. The apparatus is characterized in that the circuit device further comprises a turbine coupled to another turbine connected to the air delivery device such that the circuit can be driven by means of excess compressed airflow.

The advantage of the invention proposed here is that the circulation of the fuel in all power ranges can be operated without or with less expenditure of parasitic energy and in such a way that an improved fuel cell stack

Conversion of existing in the supplied fuel chemical energy into electrical Energy can be done. In addition, not only a lambda value of up to 8 can be safely set on the anode side in the low power range, but also spontaneously

Performance requirements are responded faster because the coupled turbines run at an increased speed and only throttle valves are to provide.

In a preferred embodiment, a corresponding mass flow of fuel, a corresponding mass flow of compressed air and a corresponding compression of the air flow are required for the provision of a respective requested power by the fuel cell stack. This is to provide the required compression

required appropriate flow of air. The motive nozzle is designed so that above a power limit of the required flow rate of fuel is sufficient to drive the circuit. Furthermore, the further turbine and the air conveying device are designed so that below the power limit to provide the required

Compaction to be compressed mass flow in air is much larger than the required

Flow of compressed air that the excess compressed air flow together with the required flow of fuel sufficient to drive the circuit.

Thus, advantageously, the drive of the circuit can be accomplished in a way that is always accompanied by an optimized supply of fresh fuel at the same time.

In particular, the circuit can be completely driven by the turbine below another lower power limit.

Namely, the lower the power to be generated, the higher is the difference between the air flow rate required for compression and the air flow rate required to generate the power to be compressed.

The device may further comprise a between the air conveying device and the

Oxygen supply arranged moisture carrier, the humidity between the required mass flow of compressed air and an exhaust air flow of the

Fuel cell stack transfers. The excess compressed air stream is then removed between the air conveyor and the moisture carrier for delivery to the further turbine. The removal of the excess compressed air flow before the moisture carrier advantageously avoids the unnecessary transmission of moisture between the

excess compressed air flow and the exhaust air flow.

According to the invention, a method according to claim 5 for operating the inventively proposed device is further presented.

The method is characterized in that below a power limit, a required to provide a power of the fuel cell stack mass flow

outflowing fuel is insufficient to drive the cycle. Therefore, the method comprises operating the air conveying device at least below the power limit, so that the flow rate of compressed air is so much greater than the mass flow of compressed air required by the fuel cell stack that the excess compressed air flow sufficient, the other turbine and thus by means of the turbine at least partially to drive so that below the power limit, the turbine together with the motive nozzle sufficiently drives the circuit.

In an advantageous embodiment, the method further comprises operating the air conveyor below another lower power limit so that the mass flow of compressed air is so much larger than the mass flow of compressed air required by the fuel cell stack that the excess compressed air flow is sufficient to completely complete the circulation by the turbine drive.

In a further advantageous embodiment, the method according to the invention can transmit moisture between the mass flow of compressed air required by the fuel cell stack and an exhaust air flow of the fuel cell stack by means of a

Moisture transfer and removal of the excess compressed air flow between the air conveyor and the moisture carrier for supply to the turbine include.

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:

Figure 1 shows an exemplary embodiment of the invention, and FIG. 2 schematically shows the profile of the setpoint value of the lambda value as a function of the requested power as well as the actual value of a generic system and the exemplary embodiment of the invention.

FIG. 1 shows an exemplary fuel cell system 10. On the anode side, a fuel cell stack 100 is superstoichiometrically supplied from a fuel reservoir 110 with compressed fuel (hydrogen as pure substance or in bound form) via lines 120, 130. Furthermore, the fuel cell stack 100 is supplied via lines 170, 180 with compressed air, which is provided by a compressor 230 driven by an electric motor, for example. Fuel and air are then converted into electrical energy in the fuel cell stack 100. Between the lines 120, 130, a jet pump with a drive nozzle 200 and downstream diffuser 300 is arranged. Gas flowing out of the fuel storage device 1 10 thus draws gas from a line 150. The line 150 is connected to the fuel cell stack 100 on the cathode side via a further line 140. Lines 140, 150, and 130 form a circuit in which fuel unreacted by the fuel cell stack 100 is recirculated into the fuel cell stack 100.

In the middle and upper power ranges, the mass flow flowing out of the fuel reservoir 110 is so great that the suction effect of the drive nozzle 200 is sufficient to maintain the circulation.

In a lower power range below a power limit, however, the suction effect is insufficient. Therefore, in the illustrated exemplary embodiment of the invention, a turbine 210 is disposed between conduits 140 and 150. In the exemplary embodiment, the turbine 210 is magnetically coupled to a turbine 220 so that the turbines 210, 220 form a double-sided turbine. Via a line 160, the turbine 220 can be acted upon by compressed air and thus driven. The turbine 210 (eg, magnetically coupled) then rotates, thus also causing recirculation of the unreacted fuel.

In the exemplary embodiment, the line 160 branches off from the line 180 at a branch 240 and thus guides part of the air compressed by the compressor 230 to the turbine 220. This is particularly advantageous because in the power range below the power limit the compressor 230 has a larger mass flow of air must be compressed than is needed for the reaction in the fuel cell stack 100, otherwise not the necessary compression can be achieved. So there is an excess flow below the power limit compressed air, which can be used advantageously for recirculation, in particular because below the power limit, the recirculating effect of the motive nozzle 200 is insufficient.

To regulate the proportions of the flow of compressed air used in the

Fuel cell stack 100 and the turbine 220 are supplied downstream of the branch 240 in the lines 160 and 180 valves 340, 350 are arranged.

Between the lines 170 and 180 is in the embodiment additionally a

Moisture transfer device 250 arranged, with the moisture between the compressed air flow and another air flow can be transmitted. In the exemplary embodiment, this additional air flow is the exhaust air flow of the fuel cell stack 100, which is supplied to the moisture carrier 250 via line 190 and discharged from there via line 260.

Furthermore, a conduit 270 discharges the air flow with which the turbine 220 is driven. Finally, a line 280, which branches off via a bleed valve 290 (purge valve) from line 240, allows the circulation of lines 130, 140, 150 to be vented.

FIG. 2 shows diagrammatically that, in particular in low power ranges, the actual value profile 510 of the air-fuel ratio (lambda) supplied to the fuel cell 100 with a generic fuel cell system equipped only with a jet pump differs significantly from the desired value profile 520. Namely, while the low power setpoint curve 520 is high

Lambda setpoints significantly greater than 1 calls, the generic fuel cell system can only generate an actual value curve 510, in which the lambda values in this power range are significantly lower than 1. The setpoint curve 520 approaches increasing

Performance requirements asymptotically set to 1. The process value curve 510 is significantly less than 1 for low power requirements, then increases to a value greater than 1, and then approaches the value 1 again. The actual value curve 510 and the setpoint course 520 intersect at a power limit. For the power range below the

Power limit, the setpoint is always greater than the actual value of a generic

Fuel cell system, which is equipped only with a jet pump. Only above the power limit of the actual value is always greater than the setpoint, but with a relatively small difference.

A system with double-sided turbine according to the present invention, however, can generate a more favorable actual value profile 530 (It should be noted that in FIG Recognizability because of course 530 with slight offset upwards). The actual value curve 530 corresponds to the setpoint course 520 below the power limit, because in this power range the double-sided turbine causes the recirculation. in the

Power range above the power limit corresponds to the actual value curve 530 the previously known Istwertverlauf 520, since in this power range, the recirculation of the motive nozzle 200 is effected.

List of Reference Devices

fuel cell stack

Storage device for compressed fuel

, 130, 140, 150, 160, 170, 180, 190, 260, 270, 280 lines driving nozzle

turbine

further turbine

compressor

diversion

Humidity transmitters

Bleed valve (purge valve)

diffuser

, 350 valves

Process value with jet pump

Setpoint curve

Actual value curve with turbine and jet pump

Claims

claims

1 . Device (10) comprising:

a compressed fuel storage device (110); and

a fuel cell stack (100) having a circulation circuit (130, 140, 150) for a fuel circuit, a line (170) for air supply and a further line (190) for air discharge, wherein in the circulation device (130, 140, 150) a drive nozzle ( 200) connected to the storage device (110) such that fuel flowing out of the storage device (110) at least partially drives the circuit;

an air conveying device (230) for providing a supply for the

Fuel cell stack (100) required compressed air flow to the line (170) for air supply, characterized in that the circulation device (130, 140, 150) further comprises a turbine (210) which is coupled to a further turbine (220), the so is connected to the air conveying device (230) that the circuit can be driven by means of an excess compressed air flow.

2. Device according to claim 1, characterized in that for the provision of a respective requested performance by the fuel cell stack (100) a

corresponding mass flow of fuel, a corresponding mass flow of compressed air and a corresponding compression of the air flow is required, wherein the provision of the required compression a corresponding mass flow of air is needed,

wherein the motive nozzle (200) is designed so that above a power limit the required mass flow of fuel is sufficient to drive the circuit,

wherein the further turbine (220) and the air conveying device (230) are designed so that below the power limit of the mass flow of air to be compressed to provide the required compression is so much greater than the required compressed air flow that the compressed compressed air flow together with the required flow of fuel sufficient to drive the cycle.

3. A device according to claim 2, characterized in that below a further lower power limit, the circuit is completely driven by the turbine (210).

4. Device according to one of the preceding claims, characterized in that the device (10) further comprises a between the air conveying device (230) and the oxygen supply (170) arranged moisture carrier (250), the humidity between the required mass flow of compressed air and a Exhaust air stream of the fuel cell stack (100) transmits, and wherein the excess compressed air flow between the air conveyor device (230) and the moisture carrier (250) for supply to the further turbine (220) is removed.

5. A method for operating a device (10) according to one of the preceding

Claims, being below a performance limit

a required for providing a power of the fuel cell stack (100)

Flow of outflowing fuel is not sufficient to drive the cycle, comprising:

Operating the air conveyor (230) at least below the power limit, so that the flow rate of compressed air is much greater than that of

Fuel cell stack (100) needed flow of compressed air that the excess compressed air flow is sufficient to drive the other turbine (220) and thereby the circuit by the turbine (210) at least partially so that below the power limit, the turbine (210) together with the motive nozzle (200) drives the circulation sufficiently.

6. The method of claim 5, characterized by operating the air conveying device (230) below another lower power limit, so that the flow rate of compressed air is so much greater than the fuel cell stack (100) required flow rate of compressed air that the excess compressed air flow sufficient to fully drive the cycle by means of the turbines (210).

7. The method according to claim 5 or 6, characterized by transfer of moisture

between the mass flow of compressed air required by the fuel cell stack (100) and an exhaust air flow of the fuel cell stack (100) by means of a moisture transfer device (250) and taking the excess compressed air flow between the

Air conveying device (230) and the moisture carrier (250) for supplying to the further turbine (220).