DE102007045278A1 - Fuel cell system and method for operating a fuel cell system - Google Patents

Abstract

The invention relates to a fuel cell system having at least one fuel cell (2) whose anode side (4) is connected to a fuel branch (6) via which fuel can be conducted to the anode side (4) with one of the fuel branch (6) at a branch (6). 9) branching off after the fuel cell (2) and into the fuel branch (6) at a junction (11) in front of the fuel cell (2) opening recirculation branch (8), and with a heat transfer device (18) which with the fuel branch (6) thermally is formed and for heating the in the fuel branch (6) flowing fuel is formed, wherein the heat transfer device (18) in the flow direction of the fuel before or at the junction (11) of the recirculation branch (8) in the fuel branch (6) with the fuel branch ( 6) is thermally coupled to heat the fuel. The invention also relates to a method for operating a fuel cell system.

Description

The The invention relates to a fuel cell system with at least one Fuel cell whose anode side is connected to a fuel branch over which fuel is conductive to the anode side, and one of the Fuel branch branching off at a branch after the fuel cell and into the fuel branch at a junction in front of the fuel cell opening recirculation branch. Furthermore, the concerns Invention a method of operating a fuel cell system with at least one fuel cell.

From the DE 102 48 611 A1 For example, a fuel cell system and a method of preheating a fuel cell are known. For preheating a fuel cell stack in a cold start or frost conditions, the compressed air from a compressor with the heat stored therein is used to heat the fuel cell stack and preheat hydrogen gas which is transferred into the fuel cell stack. For this purpose, a heat exchanger can be provided, which is coupled with a line branch, which leads from a compressor to a cathode side of the fuel cell, on the one hand, and a line, which leads from the hydrogen tank to the anode side of the fuel cell, on the other hand. The fuel cell system may further include exhaust and / or return piping systems for treating and / or removing exhaust gases from the vehicle and / or returning unused hydrogen gas to the fuel cells.

It Object of the present invention is a fuel cell system and to provide a method in which the operation in particular improved at low temperatures and thus the starting behavior can be.

These Task is by fuel cell systems, which the characteristics according to claim 1 or 8, and a method which the Features according to claim 13, solved.

One The first aspect of the invention relates to a fuel cell system with at least one fuel cell, the anode side with a Fuel branch is connected, about which fuel can be conducted to the anode side. In addition, the fuel cell system includes a recirculation branch for exhaust gas recirculation, which branches off from the fuel branch at a branch after the fuel cell and which in the fuel branch at a junction opens in front of the fuel cell. Furthermore, the Fuel cell system, a heat transfer device which is thermally coupled to the fuel branch and for heating the fuel flowing in the fuel branch is trained. The heat transfer device is in the flow direction of the fuel before or at the Entry of the recirculation branch into the fuel branch with fuel branch for heating of fuel thermally coupled.

Especially is in the fuel branch before the confluence or directly arranged at the confluence with a metering unit. With this can the flowing from a fuel tank Fuel to be metered to the anode side of the fuel cell. Is the fuel cell system shut down and at low temperatures, especially cooled to temperatures below 0 ° C, Water can condense on the dosing unit or through shutdown processes Water are introduced into the metering and freeze there. This is the flow of fuel after the restart of the fuel cell system reduced.

If the then supplied from the fuel tank fresh Fuel is cold enough, thawing of the dosing into the prevented introduced water. By heating the Fuel at temperatures <0 ° C will quickly thaw the frozen water in the dosing unit or at the mixing point and thus at the confluence of the recirculation branch in the fuel branch allows, so the specific maximum flow area can be provided can.

in the In the case of a two- or multi-stage dosing unit, water, the at the unused dosing component at the dosing point freezes as a result of the cold fuel supplied and cause a malfunction of the dosing.

in the Operation, the fuel cell system heats up within a short time after starting. But as long as cold fuel, which has assumed the temperature of the environment, is metered in, falls at the mixing point and thus also at the confluence of a recirculation branch in a fuel branch temperature and Water falls out. By preheating the fuel according to the Fuel cell system according to the invention can this attack of liquid water is reduced or even completely avoided. Freezing the dosing unit in particular at the mixing point in the area of the confluence of the recirculation branch can be prevented.

additional Heating elements for heating the passing point are thus to thaw out frostbite in this area no longer necessary.

Particularly preferred may be by the heat transfer device with its specific Arrangement in the fuel cell system heating of the fuel to temperatures <0 ° C can be achieved, which in particular the thawing of frozen metering units and / or mixing points can be made possible.

Preferably is the heat transfer device with the fuel branch and thermally coupled to the recirculation branch. This can be a Achieved effective heat transfer to the fuel become.

Especially is the heat transfer device in the flow direction of the gas in the recirculation branch before one in the recirculation branch arranged separator thermally coupled to the recirculation branch.

It can also be provided that the heat transfer device in the flow direction of the gas in the recirculation branch a arranged in the recirculation branch separator with this Rezirkulationszweig is thermally coupled.

Especially can also be provided that in the recirculation branch a blower is arranged and the thermal coupling of the heat transfer device with the recirculation branch in the flow direction of the gas is formed after the blower. By this configuration the waste heat of the blower can be used, to heat the fuel.

About that In addition, in such a thermal coupling with the recirculation branch also the waste heat of the fuel cell itself for heating be used of the fuel.

The Heat transfer device may be a heat exchanger exhibit. In particular, the heat transfer device comprises only this heat exchanger. The fuel can thereby over a Cooling circuit (high or low temperature cooling circuit) be heated by the heat exchanger.

Of the Heat exchanger for heating the fresh fuel, especially the fresh hydrogen, can in the fuel cell system thus be used in different positions and so in addition have a positive influence on system behavior.

is the heat transfer device in the flow direction of the gas in the recirculation branch in front of the separator, Thus it can be achieved that the dew point in the dosing unit or the mixing point at the confluence of the recirculation branch is shifted in the fuel branch in front of the separator.

The Heat transfer device may also be an electrical Have heating unit. It can also be provided that the heat transfer device at least one heat exchanger and at least one electrical Heating unit includes.

The Heat transfer device can instead of a thermal coupling with the recirculation branch to produce a Heat input into the fuel in the fuel branch with the fuel cell and / or a cooling circuit and / or be coupled to an electric heating unit. A heat input can also be powered by a blower or a compressor heated air and / or by catalytic combustion of Hydrogen occur.

Preferably is the heating of the fuel depends on the temperature in the recirculation branch and / or dependent from the temperature at the confluence of the recirculation branch into the fuel branch feasible. The warming of the fresh fuel can thus be temperature controlled or temperature controlled be and depending on at least one of the above specific temperatures in the branches.

It can be provided that the heating of the fuel operating phase specific is performed. Especially is the heating of the fuel in a cold start phase provided of the fuel cell system. It can also be provided be that the heating of the fuel, at least temporarily even after the cold start phase in normal operation of the fuel cell system is carried out.

All Generally, with the fuel cell system according to the invention a fast thawing of ice particles at specific locations in the Fuel branch can be achieved. In addition, the water loss can at the metering point of the fresh fuel, in particular hydrogen, be reduced. In addition, can constant Operating conditions are achieved and the design of components, in particular a pressure control valve for pressure control of the fuel tank in the fuel cell flowing fuel can be improved become. Currently, a design of this pressure control valve for Fuel temperatures from -25 ° C to + 85 ° C required, which is due to the embodiment of the invention System is no longer required and this value interval is reduced can be. Due to a relatively constant gas inlet temperature the humidity in the recirculation branch can be better controlled and a condensing out of water, as in cold, freshly fed Fuel would be the case, can be avoided or minimized become.

One Another aspect of the invention relates to a fuel cell system with at least one fuel cell, the anode side with a Fuel branch is connected, about which fuel can be fed to the anode side. The fuel cell system comprises Furthermore, a recirculation branch, which of the fuel branch branches off at a branch after the fuel cell and into the fuel branch opens at an entrance in front of the fuel cell. The fuel cell system further includes a bypass, which passed around the fuel cell, wherein the bypass designed in such a way is that through him a heated by a heat source Medium for heating the fuel and / or a Fuel branch and / or the recirculation branch associated component is conductive. By this configuration can advantageously the efficient and relatively low-cost heating of frozen Components of the fuel cell system are made possible. In addition, also by the execution the heating of the fresh incoming fuel be achieved.

Preferably the heat source has a fuel branch arranged in the electric heating unit on. The heat introduced by the heater can then bypass the still frozen fuel cell effectively arrive at the remaining existing in the anode circuit components and Thaw them faster.

It can also be provided that the heating unit in the flow direction fuel before an entrance of a recirculation branch is arranged in the fuel branch. Just the confluence the recirculation branch, preferably a dosing unit can be arranged through the bypass especially be effectively acted upon with warm gas, and thus an effective Thawing just this particular component can be achieved.

Preferably the heat source has a compressor, which with coupled to the bypass and for generating the heated medium is trained. As a result, the resulting in the air compression Heat are introduced into the fuel circuit and there Thawing of frostbite in the form of ice cause. By the Bypass can be achieved by otherwise using as a heat sink serving fuel cell is bypassed and the thawing of frozen Components can be done much faster.

at the other option about the introduction of heat over the compressed air can do this in particular without an additional Heat exchangers take place and an effective heating of the fuel circuit be enabled.

Preferably the bypass is only in specific operating phases, in particular in the cold start phase of the system, to flow through the heated medium released. Optimized operation can thereby heating is possible and in particular in other phases of operation then the operation is possibly not adversely affected.

About that In addition, it can also be provided that parts of the fuel tank are heated. For example, here below other high-pressure fuel lines and valves are heated.

at a method according to the invention for operating a fuel cell system having at least one fuel cell is used to heat the flowing in a fuel branch Fuel and / or for heating a fuel branch associated component and / or one of the fuel branch branching off after the fuel cell and before the fuel cell in the fuel branch opening recirculation branch associated component generated by a heat source heated medium by a guided around the fuel cell Bypass passed. By this configuration, a highly effective heating be achieved and the operation of the fuel cell system in particular in a cold start phase, in which the freshly supplied fuel would be relatively cool and / or components of the anode branch are at least partially frozen, to be improved.

advantageous Embodiments of the fuel cell systems according to the invention are as advantageous embodiments of a method according to the invention to watch.

embodiments The invention will be described in more detail below with reference to schematic drawings explained. Showing:

1 a first embodiment of a fuel cell system according to the invention;

2 A second embodiment of a fuel cell system according to the invention;

3 A third embodiment of a fuel cell system according to the invention; and

4 A fourth embodiment of a fuel cell system according to the invention.

In The figures are the same or functionally identical elements with the provided the same reference numerals.

In 1 is a schematic representation of a fuel cell system 1 shown, which is designed as a mobile fuel cell system and can be used in a vehicle. The fuel cell system 1 includes at least one fuel cell 2 , in particular a fuel cell stack with a plurality of such fuel cells 2 , The fuel cell 2 is designed in the embodiment as a PEM fuel cell and comprises a cathode space or a cathode side 3 passing through a membrane 5 from an anode space or an anode side 4 is separated.

The fuel cell system 1 includes a fuel branch 6 with a fuel container 7 in which the fuel is hydrogen or a hydrogen-containing gas. In addition, the fuel branch includes 6 one from the container 7 to the anode side 4 leading supply line 12 and one from the anode side 4 laxative exhaust pipe 10 ,

Furthermore, the fuel cell system 1 a recirculation branch 8th on, which is at the junction 9 from the exhaust pipe 10 branches off and at the junction 11 in the supply line 12 opens. In the recirculation branch 8th is a fan 13 arranged, and exhaust of the anode side 4 will be returned.

Furthermore, the fuel branch is 6 a dosing unit 14 assigned, which in the exemplary embodiment two parallel dosing components 15 and 16 , in particular flow / pressure control valves. The dosing unit 14 especially at the confluence 11 be arranged and thus positioned at the mixing point of the system.

In addition, in the feed line 12 a shut-off unit 17 , in particular a valve arranged. The shut-off unit 17 may additionally or instead of their functionality to shut off also be designed for pressure control of the fuel. In the embodiment, the shut-off is 17 in the flow direction of the fuel in the fuel branch 6 in front of a heat transfer device 18 arranged. It can also be provided that the shut-off 17 after the heat transfer device 18 is arranged.

Im in 1 the embodiment shown is the heat transfer device 18 with the fuel branch 6 before the confluence 11 thermally coupled. It can also be provided that the heat transfer device 18 at the junction 11 with the fuel branch 6 thermally coupled.

The heat transfer device 18 includes a heat exchanger 19 , which in addition to the thermal coupling with the fuel branch 6 on the other hand thermally coupled with another heat source. For example, the further coupling 20 with the fuel cell 2 and / or a cooling circuit of the vehicle and / or an electric heating unit and / or heated air and / or a combustion device for the catalytic combustion of hydrogen, may be provided.

It can in the embodiment according to 1 However, also be provided that the heat transfer device 18 only comprises an electric heating unit, which at the appropriate place in the fuel cell system 1 in the fuel branch 6 is involved. The heat transfer device 18 is for heating in the fuel branch 6 flowing fuel formed. By the heat transfer device 18 that will be over the container 7 freshly supplied fuel in the fuel branch 6 warmed to a temperature> 0 ° C and an at least partially frozen metering unit 14 and / or junction 11 Can be effectively thawed during operation. In particular, this is advantageous in a cold start phase of the system.

In 2 is another embodiment of a fuel cell system 1 shown in which, in contrast to the embodiment according to 1 the heat exchanger 19 the heat transfer device 18 with the fuel branch 6 on the one hand and with the recirculation branch 8th on the other hand is thermally coupled. Moreover, in the recirculation branch 8th next to the blower 13 a separator 21 in the flow direction of the gas in the recirculation branch 8th in front of the blower 13 arranged. The thermal coupling of the heat exchanger 19 with the recirculation branch 8th is after the blower 13 intended. In particular, the thermal coupling of the heat exchanger 18 with the recirculation branch 8th after the separator 21 realized.

However, it may also be provided, as indicated by the dashed line of the heat exchanger 19 ' in 2 is indicated that the thermal coupling with the recirculation branch 8th in front of the separator 21 is realized.

Both in the execution according to 1 as well as in the statements according to 2 can be provided that the heat transfer device 18 in addition to the heat exchanger 19 respectively. 19 ' having an electric heating unit. Preferably, this is for example the heat exchanger 19 formed on the side on which the thermal coupling with the fuel branch 6 is realized.

Preferably, the heating of the fuel, which takes place via the container 7 is supplied fresh, temperature-controlled or temperaturge controls and in particular depending on the temperature of the recirculation branch 8th flowing gas and / or depending on the temperature of the at the confluence 11 flowing gas.

Another embodiment of a fuel cell system 1 is in 3 shown. In this embodiment, the metering unit 14 at the junction 11 arranged, in which connection the dosing unit 14 for example, may be a three-way valve. In addition, in the fuel branch 6 in the flow direction of the fuel before the confluence 11 an electric heating unit 26 arranged. In addition, the fuel cell system includes 1 a bypass 22 , which in the direction of flow of the fuel at the junction 23 from the supply line 12 branches off and after the fuel cell 2 at the junction 24 in the exhaust pipe 10 opens. The confluence 24 can with the diversion 9 of the recirculation branch 8th from the exhaust pipe 10 coincide. However, this can also be otherwise formed.

In the bypass 22 is a shut-off unit 25 , in particular a shut-off valve, arranged.

In addition, in the exhaust pipe 10 in the flow direction of the exhaust gas after the confluence 24 and the turnoff 9 a valve 27 arranged.

The bypass 22 is about the fuel cell 2 guided and designed so that a generated by a heat source and warm medium, in particular a gas for heating the fuel and / or a fuel branch 6 and / or the recirculation branch 8th assigned component is conductive. The heat source is in the in 3 shown embodiment, the electric heating unit 26 ,

Will the fuel cell system 1 shut down and exposed to low ambient temperatures, so can freeze different components in the fuel branch 6 and / or in the recirculation branch 8th accompanied. In particular, in a cold start phase can then by the heating unit 26 Heat are introduced, which then bypassing the still frozen fuel cell 2 over the bypass 22 to the remaining components in the fuel circuit 6 and in the recirculation circuit 8th can be performed, which can be thawed faster. In particular, in such a cold start phase is thus the shut-off 25 open.

In 4 is another embodiment of a fuel cell system 1 shown in which, in contrast to the embodiment according to 3 the electric heating unit 26 not available. Rather, in this embodiment, the air heated by a compressor or compressor, not shown, directly into the fuel branch 6 and the recirculation branch 8th brought in. This is done by allowing this heated air through the valve 27 into the respective branches 6 and 8th is directed. In addition, then here is the shut-off 25 open so that the heated air is first in the fuel branch 6 and in the recirculation branch 8th Thaw existing components. The gas can then be retrofitted via the separator 21 from the recirculation circuit 8th be removed. This is on the separator 21 a corresponding outlet provided.

In all embodiments can also be provided that in addition also other parts are heated, in particular, for example, the container 7 ,

1

The fuel cell system

2

fuel cell

3

cathode side

4

anode side

5

membrane

6

fuel branch

7

container

8th

Rezirkulationszweig

9

diversion

10

exhaust pipe

11

junction

12

feed

13

fan

14

dosing

15 16

metering components

17

Shut-off

18

Heat transfer device

19 19 '

heat exchangers

20

coupling

21

separators

22

bypass

23

diversion

24

junction

25

Shut-off

26

heating unit

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 10248611 A1 [0002]

Claims (13)

Fuel cell system with at least one fuel cell ( 2 ), whose anode side ( 4 ) with a fuel branch ( 6 ), via which fuel to the anode side ( 4 ) is supplied with one of the fuel branch ( 6 ) at a branch ( 9 ) after the fuel cell ( 2 ) branching off and into the fuel branch ( 6 ) at a junction ( 11 ) in front of the fuel cell ( 2 ) recirculation branch ( 8th ), and with a heat transfer device ( 18 ), which with the fuel branch ( 6 ) is thermally coupled and for heating in the fuel branch ( 6 ) is formed, characterized in that the heat transfer device ( 18 ) in the direction of flow of the fuel before or at the junction ( 11 ) of the recirculation branch ( 8th ) into the fuel branch ( 6 ) with the fuel branch ( 6 ) is thermally coupled to heat the fuel. Fuel cell system according to claim 1, characterized in that the heat transfer device ( 18 ) with the fuel branch ( 6 ) and the recirculation branch ( 8th ) is thermally coupled. Fuel cell system according to claim 1 or 2, characterized in that the heat transfer device ( 18 ) in the flow direction of the gas in the recirculation branch ( 8th ) in front of a in the recirculation branch ( 8th ) arranged separators ( 21 ) with the recirculation branch ( 8th ) is thermally coupled. Fuel cell system according to one of claims 1 or 2, characterized in that the heat transfer device ( 18 ) in the flow direction of the gas in the recirculation branch ( 8th ) after one in the recirculation branch ( 8th ) arranged separators ( 21 ) with the recirculation branch ( 8th ) is thermally coupled. Fuel cell system according to one of the preceding claims, characterized in that the heat transfer device ( 18 ) a heat exchanger ( 19 ) having. Fuel cell system according to one of the preceding claims, characterized in that the heat transfer device ( 18 ) has an electric heating unit. Fuel cell system according to one of the preceding claims, characterized in that the heating of the fuel depends on the temperature in the recirculation branch ( 8th ) and / or the temperature at the junction ( 11 ) is feasible. Fuel cell system with at least one fuel cell ( 2 ), whose anode side ( 4 ) with a fuel branch ( 6 ), via which fuel to the anode side ( 4 ) and one of the fuel branch ( 6 ) at a branch ( 9 ) after the fuel cell ( 2 ) branching off and into the fuel branch ( 6 ) at a junction ( 11 ) in front of the fuel cell ( 2 ) recirculation branch ( 8th ), characterized in that a bypass ( 22 ) around the fuel cell ( 2 ), through which one of a heat source ( 26 ) heated medium for heating the fuel and / or a fuel branch ( 6 ) and / or the recirculation branch ( 8th ) associated component is conductive. Fuel cell system according to claim 8, characterized in that the heat source in the fuel branch ( 6 ) arranged electrical heating unit ( 26 ) having. Fuel cell system according to claim 9, characterized in that the heating unit ( 26 ) in the flow direction of the fuel before the confluence ( 11 ) of the recirculation branch ( 8th ) into the fuel branch ( 6 ) is arranged. Fuel cell system according to one of claims 8 to 10, characterized in that the heat source comprises a compressor, which with the bypass ( 22 ) and is designed to produce the heated medium. Fuel cell system according to one of claims 9 to 12, characterized in that the bypass ( 22 ) is released only for specific operating phases, in particular in the cold start phase of the system, for flowing through the heated medium. Method for operating a fuel cell system ( 1 ) with at least one fuel cell ( 2 ), in which for heating in a fuel branch ( 6 ) flowing fuel and / or for heating a fuel branch ( 6 ) associated component and / or one of the fuel branch ( 6 ) after the fuel cell ( 2 ) branching off and in front of the fuel cell ( 2 ) into the fuel branch ( 6 ) recirculating branch ( 8th ) associated component from a heat source ( 26 heated by a to the fuel cell ( 2 ) guided bypass ( 22 ).