Title of Invention

FUEL CELL SYSTEM AND METHOD FOR GENERATING ELECTRICAL ENERGY BY MEANS OF A FUEL CELL SYSTEM

Abstract The present invention relates to a fuel cell system, in particular as a drive system for a motor vehicle. This fuel cell system is more economical and environmentally friendly for the generation of electrical energy for a drive system of a motor vehicle, with high efficiency and small space requirement. The fuel cell system having an autothermal reformer unit (18) for producing hydrogen from a raw material (28) for operating a downstream fuel cell unit (10), an oxidation device (34) for converting carbon monoxide into carbon dioxide being arranged between the reformer unit (18) and the fuel cell unit (10). In this case, a water injection device (46) is provided at the oxidation unit (34) and injects water into the latter. (Fig. 1)
Full Text The invention relates to a fuel cell system, in particular as a drive system for a motor vehicle, having a reformer unit for producing hydrogen from an energy source, in particular a liquid raw material with the supply of air for operating a downstream fuel cell unit, an oxidation device for converting carbon monoxide into carbon dioxide being arranged between the reformer unit and the fuel cell unit. The invention furthermore relates to a method for generating electrical energy by means of a fuel cell system, in particular for a drive system of a motor vehicle, hydrogen being produced in a reformer process from a raw material with the supply of air in order to operate a fuel cell unit, carbon monoxide being oxidized to form carbon dioxide downstream of the reformer process and upstream of the fuel cell unit.
EP 0 217 532 discloses a catalytic hydrogen generator which produces hydrogen in an autothermal reformer unit from a methanol/air mixture. In this case, a thermocouple is arranged in the reformer unit and controls air supply into the methanol/air mixture in such a way that the supply of air is reduced with increasing temperature at the position of the thermocouple in the reformer.
In a refinement of this arrangement, WO 96/00186 describes a hydrogen generator, the catalyst being arranged around an inlet tube for the methanol/air mixture in such a way that the methanol/air mixture flows radially through the catalyst.
D 43 45 319 C2 and D 43 29 323 C2 describe a fuel cell electrical generation system, hydrogen being produced from a methanol/water mixture in a reformer unit. This hydrogen is supplied to a downstream fuel cell in order to generate electrical energy. In order to produce sufficient heat in the reformer, some of the methanol is not supplied to the methanol/water mixture but instead is burnt in an extra burner.
DE 196 29 084 Al discloses an electrical vehicle with a drive battery made up of fuel cells, the fuel cells being arranged in such a way that they are cooled by the air flow due to the motion of the vehicle.
The article "Heureka?" [Eureka] in DE-Z Autotechnik No.5/1997, pages 20/21 describes a motor vehicle with fuel cell drive, the hydrogen needed for operating the fuel cells being obtained in the vehicle itself from petrol. In this case, the petrol is converted into hydrogen in a multistage process. Prior to the conversion, the petrol is brought into the gas state by heating in an evaporator. In a partial combustion reactor, with an oxygen deficit, hydrogen and carbon monoxide are produced. In order to oxidize the carbon monoxide, copper oxide and zinc oxide catalysts are provided, water vapour being supplied as an oxygen source for the reaction. In a further step, an approximately 1% final fraction of carbon monoxide is post-combusted in a conventional platinum oxidation catalyst with a supply of air. The mixture obtained in this way of hydrogen, carbon monoxide and carbon dioxide still contains 10 ppm of carbon monoxide, which is safe for a downstream fuel cell. After cooling to about 80 degrees Celsius in a heat exchanger, the gas is therefore delivered to the fuel cell.
The article "Alternative Fuel" in the JP journal Asia-Pacific Automotive Report, 20.01.1998 Vol. 272 pages 34 to 39 discloses a similar fuel cell system for motor vehicles, a methanol reformer unit being provided for
producing hydrogen for a fuel cell. In this case, the water produced during the electrochemical reaction of hydrogen and oxygen is reused for the reformer process. For the reformer process, deionized water and methanol are mixed, evaporated and converted into hydrogen and carbon dioxide at a temperature of 250 degrees Celsius. This hydrogen is supplied to a fuel cell which converts it, together with atmospheric oxygen, into electrical energy and water in a catalytic process. The heat energy needed for the evaporation and for the reformer process is generated in a catalytic burner which is downstream of the fuel cell and is operated with residual gas from the fuel cell. This gas contains hydrogen, since the fuel cell arrangement utilizes only about 75% of the hydrogen suppl ied. I f not enough residual hydrogen is available for the catalytic burner, methanol from the fuel tank is used to obtain heat for the reformer. Before the introduction of the gas which is produced in the reformer and has a hydrogen component, this gas is purified by means of a catalytic reaction, carbon monoxide being converted into carbon dioxide. In an embodiment presented for a fuel cell system of a motor vehicle, the methanol reformer comprises an evaporator, a reformer and an oxidation unit for carbon monoxide.
DE 43 22 765 CI describes a method and a device to dynamically control power for a motor vehicle with a fuel cell which delivers electrical energy to an electrical drive unit. On the basis of a power demand corresponding to an accelerator pedal position, an air mass flow is calculated which is needed for the fuel cell to provide a corresponding target power. A compressor arranged in an intake line of the fuel cell has its rotational speed controlled according to the air flow required.
EP 0 629 013 Bl discloses a method and a device for the air feed of a fuel cell system. In this case, process
air is compressed by means of a compressor before it enters a corresponding fuel cell. After it has flowed through the fuel cell, the exhaust air released is expanded through a turbine in order to recover energy, the turbine, the compressor and an extra drive motor being arranged on a common shaft. The compressor is designed such that its rotational speed can be varied and is arranged on a common shaft with an expander as a turbine for expanding the exhaust air. Through the use of an expander with variable absorption capacity, the air flow for the fuel cell is controlled.
WO 97/16648 discloses a screw compressor for a refrigerator. This screw compressor comprises two pump chambers, an outlet of a first pump chamber being connected to a secondary inlet of a second pump chamber.
The object of the present invention is to further develop a fuel cell system of the type mentioned above in such a way as to enable more economical and more environmentally friendly use for the generation of electrical energy, in particular for a drive system of a motor vehicle, with high efficiency and small space requirement.
This object is achieved according to the invention by a fuel cell system of the aforementioned type having the characterizing features as described herein and by method of the aforementioned type with the characterizing features as described. Advantageous refinements of the invention are also as described herein.
To that end, it is proposed in a fuel cell system according to the invention that a water injection device is provided at the oxidation unit, which device injects water into the latter.
This has the advantage that, at the same time as carbon monoxide is removed from a process gas from the reformer unit with high hydrogen content for the fuel cell unit, sufficient cooling or precooling takes place so that the process gas can be delivered to the fuel cell unit without an expensive cooling device, or with a correspondingly inexpensive cooling device. Furthermore, the injected water also provides the oxygen needed for the oxidation of carbon monoxide, hydrogen also being released at the same time by this oxidation reaction, so that a separate oxygen supply for the oxidation device can be reduced in quantity and, at the same time, there is an increased hydrogen content in the process gas. For equal power, the fuel cell system can have its size reduced owing to the extra hydrogen enrichment in the oxidation device. This correspondingly reduces the space required and the equipment cost of the fuel cell system.
In a preferred embodiment, the reformer unit has a mixer for the raw material and a substance containing oxygen, in particular water and/or air.
A closed water circuit without the need to carry large quantities of water for the reformer process is achieved in that a water separation device, in particular a condenser, which separates water contained in the corresponding waste gas and supplies a water storage device upstream of the autothermal reformer unit, is provided in an exhaust gas flow from a cathode of the fuel cell unit and/or in an exhaust gas flow from an anode of the fuel cell unit.
In an advantageous embodiment, a separate water circuit is provided which cools the water separation devices, the fuel cell unit, an air feed to a cathode of the fuel cell unit and/or an air feed to the reformer unit-
In order to generate corresponding heat energy needed for the reaction in the reformer unit, a catalytic burner is provided which burns exhaust gas from an anode of the fuel cell unit and supplies corresponding waste heat to the reformer unit via a heat exchanger.
Alternative heat generation for the reformer unit is achieved in that the catalytic burner is connected to a storage container for the raw material.
Energy recovery is achieved in that an expander is provided in an exhaust gas flow from a cathode of the fuel cell unit and a compressor, in particular a two™ stage compressor, is provided in a feeder flow to the fuel cell unit, the expander and compressor being arranged on a common shaft.
Such a two-stage compressor makes the fuel cell system more environmentally friendly and improves its efficiency, by making two tappable air pressures with different level available to the rest of the system. A relatively low pressure is applied to the cathode of the fuel cell unit via a first stage, whereas the second stage, provided with a higher pressure, is firstly supplied to the reformer unit and, because of its relatively high pressure level, compensates for the pressure losses in the further path to the extent that the fuel cell unit has approximately the same pressure applied to it on the anode side and on the cathode side.
Expediently, the raw material is a substance containing hydrogen, in particular methanol or petrol.
In a method of the aforementioned type, it is proposed according to the invention that water is injected during oxidation of carbon monoxide to form carbon dioxide.
This has the advantage that, at the same time as carbon monoxide is removed from a process gas from the reformer process with high hydrogen content for the fuel cell unit, sufficient cooling or precooling takes place so that the process gas can be delivered to the fuel cell unit without an expensive cooling device, or with a correspondingly inexpensive cooling device. Furthermore, the inj ected water also provides the oxygen needed for the oxidation of carbon monoxide, hydrogen also being released at the same time by this oxidation reaction, so that a separate oxygen supply for the oxidation device can be reduced in quantity and, at the same time, there is an increased hydrogen content in the process gas. For equal power, the fuel cell system can have its size reduced owing to the extra hydrogen enrichment in the oxidation device. This correspondingly reduces the space required and the equipment cost of the fuel cell system.
For high efficiency of the water supply, the water is injected in vapour form or aerosol form.
An extra increase in efficiency of the fuel cell unit can be achieved in that compressed air is supplied to a process gas between the oxidation of carbon monoxide and the fuel cell unit and/or to a cathode of the fuel cell unit.
A closed water circuit without the need to carry large quantities of water for the reformer process is achieved in that water is separated from an exhaust gas flow from a cathode of the fuel cell unit and/or from an exhaust gas flow from an anode of the fuel cell unit and is supplied to the reformer process.
In order to generate corresponding heat energy needed for the reaction of the reformer process, an exhaust gas from an anode of the fuel cell unit is burnt and
corresponding waste heat is supplied to the reformer process.
Alternative heat generation for the reformer unit is achieved in that raw material is burnt and corresponding heat energy is supplied to the reformer process.
Expediently, the raw material is a substance containing hydrogen, in particular methanol or petrol.
Other features, advantages and advantageous refinements of the invention are described herein, by the following description of the invention with reference to figure 1 of the accompanying drawing. The latter shows a block circuit diagram of a preferred embodiment of a fuel cell system according to the invention.
In this fuel cell system, hydrogen for a fuel cell unit 10 having an anode 12, a cathode 14 and a heat sink 16 is produced by means of an autothermal reformer unit 18 which comprises a mixer 20, a heat exchanger 22, an evaporator 24 and a catalytic reformer 26. In order to produce hydrogen, for example methanol is supplied as raw material from a methanol tank 28 to the mixer 20, and water from a water tank 30. In the evaporator 24, the mixture of methanol and water is evaporated, and in the catalytic reformer 26 a process gas in the form of a raw gas 32 with high hydrogen content is produced in a catalytic reaction.
This raw gas contains, amongst other things, carbon monoxide (CO) which needs to be removed before delivery to the fuel cell unit 10. To that end, the raw gas 32 is delivered to an oxidation unit 34 where, with air being supplied via a line 36, the carbon monoxide is oxidized to form carbon dioxide (C02), so as to give a CO level below 20 ppm. At the same time, water from the water tank 30 is supplied via a line 44, the wate
supplied being injected into the oxidation unit 34 using an injection device 46. This leads to simultaneous cooling of the process gas in the oxidation unit 34. This fresh gas 38 produced and cooled in this way has water removed from it in an anode-gas condenser 40 and fed back to the water tank 30 via a line 42. Next, the fresh gas 38 with a high hydrogen content is delivered to the anode 12 of the fuel cell unit 10, The fresh gas 38 contains for example 50% H2, 25% N2 and 25% C02 at a temperature of about 180 to 2 00 degrees Celsius. In the anode-gas condenser 40, it is further cooled to for example about 85 degrees Celsius before being delivered to the anode 12.
On the cathode side 14, compressed air is supplied to the fuel cell unit 10 via a line 48 from a two-stage screw compressor 50. All the air lines are indicated in the Fig. by dashed lines. In this way, the fuel cell unit produces electrical energy in the known way by means of the reaction
which electrical energy can be drawn from the electrodes 12, 14 and can be supplied to an electric motor 52. The two-stage screw compressor 50 comprises a f irst stage 54 at, for example, about 3 bar pressure for the cathode 14 and a second stage 56 at, for example, 3.7 bar pressure for the combustible gas, that is to say the dehydrated fresh gas 38, to be supplied to the anode 12. By means of another take-off on the screw compressor 50, compressed air is supplied to the fresh gas 38 via a line 58 downstream of the anode gas condenser 40.
A water separator 62, which separates water from the anode exhaust gas 60 and supplies it via a line 64 to the water tank 30, is arranged in the anode exhaust gas
flow 60. A' condenser 68, which draws water from the cathode exhaust gas 66 and supplies it via a line 70 to the water tank 30, is arranged in the cathode exhaust gas flow 66. In this way, a closed water circuit is formed for the process gas, so that large amounts of water do not need to be carried for the production of hydrogen in the reformer unit 18.
For cooling of the air supply to the mixer 20, of the anode-gas condenser 40, of the water separator 62, of the condenser 68 and of the air supply 48 to the cathode 14, a separate water circuit 72 is provided, which is indicated by wavy lines. This separate water circuit 72 comprises a cooling-water container 74, a water container with deionization 76 and corresponding heat exchangers 78 and 80, respectively in the air supply 48 to the cathode 14 and in the air supply to the mixer 20.
The anode exhaust gas flow 60 flows into a catalytic burner 82 in which the anode exhaust gas 60 is further burnt with the generation of heat energy. This heat energy is forwarded to the evaporator 24 and the catalytic reformer 26 by means of the heat exchanger 22, and there sustains the catalytic reaction for the production of hydrogen. Air is supplied to the catalytic burner 82 via a line 84, Downstream of the catalytic burner 82, water from the water tank 3 0 is supplied to the anode gas 60 optionally via a line 86. Via a line 88, methanol can be selectively supplied to the catalytic burner 82 from the methanol tank 28, so that even if there is an insufficient anode exhaust gas flow 60, for example when the fuel cell system is being started up, sufficient generation of heat energy for the reformer unit 18 is ensured.
The cathode exhaust gas flow 66 is cooled in a heat exchanger 90 of the separate water circuit 72, and is subsequently set in thermal communication with the
anode exhaust gas flow 60 via a heat exchanger 92, before the two exhaust gas flows 60 and 66 leave the
system.
The cathode exhaust gas flow 66 is in this case fed through an expansion turbine 94 which, together with a compressor 96 which is intended to take in air 98 and is provided as an input stage upstream of the two-stage compressor 50, is arranged on a common shaft 100. By means of this, energy contained in the cathode exhaust gas flow 66 is recovered for compression of air 98 in the compressor 96.
A particular advantage of this embodiment, through high efficiency and low space requirement and low equipment outlay results in the combination of the two-stage compressor 50, the autothermal reformer unit 18 with the additional water injection 46 for cooling in the selective oxidation of the carbon monoxide (CO) in the oxidation unit 34 together with an independent water circuit 30, 40, 42, 62, 64, 68, 70.




WE CLAIM :
1. Fuel cell system, in particular as a drive system for a motor vehicle, having a
reformer unit (18) for producing hydrogen from an energy source, in particular a
liquid raw material (28) for operating a downstream fuel cell unit (10) , an oxidation
device (34) for converting carbon monoxide into carbon dioxide being arranged
between the reformer unit (18) and the fuel cell unit (10), characterized in that a water
injection device (46) is provided at the oxidation device (34) and injects water into the
latter.
2. Fuel cell system as claimed in claim 1, wherein the reformer unit (18) has a mixer (20) for the raw material (28) and a substance (30) containing oxygen, in particular water and/or air.
3. Fuel cell system as claimed in claim 1 or 2, wherein a two-stage compressor (50) is provided which supplies compressed air to a process gas (38) between the oxidation device (34) and the fuel cell unit (10) and/or a cathode of the fuel cell unit (10).
4. Fuel cell system as claimed in any one of the claims 1 to 3, wherein a water separation device (40, 62, 68), in particular a condenser, which separates off water contained in the corresponding gas (38, 60, 66) and supplies a water storage device (30) upstream of the autothermal reformer unit (18), provided in a fresh gas flow (38) from the oxidation unit (34) and/or in an exhaust gas flow (60) from an anode (12) of the fuel cell unit (10) and/or in an exhaust gas flow (66) from a cathode (14) of the fuel cell unit (10).
5. Fuel cell system as claimed in claim 4, wherein a separate water circuit (72) is provided which cools at least one of the water separation devices (40, 62, 68), the fuel cell unit (10, 16) and an air feed (48) to a cathode (14) of the fuel cell unit (10) and/or an air feed to the reformer unit (18, 20).
6. Fuel cell system as claimed in any one of the claims 1 to 5, wherein a catalytic burner (82) is provided which burns exhaust gas (60) from an anode (12) of the fuel cell unit (10) and supplies corresponding waste heat to the reformer unit (18) via a heat exchanger (22).
7. Fuel cell system as claimed in claim 6, wherein the catalytic burner (82) is connected to a storage container (28) for the raw material.
8. Fuel cell system as claimed in any one of the claims 1 to 7, wherein an expander (94) is provided in an exhaust gas flow (66) from a cathode (14) of the fuel cell unit (10) and a compressor (96), in particular a two-stage compressor (50), is provided in a feeder flow (98) to the fuel cell unit (10), the expander (94) and compressor (96) being arranged on a common shaft (100).
9. Fuel cell system as claimed in any one of the claims 1 to 8, wherein the raw material (28) is a substance containing hydrogen, in particular methanol or petrol.
10. Method for generating electrical energy by means of a fuel cell system, in particular for a drive system of a motor vehicle, comprising the steps of:
producing hydrogen in a reformer process from a raw material in order to operate a fuel cell unit,
oxidizing carbon monoxide to form carbon dioxide downstream of the reformer process and upstream of the fuel cell unit,
characterized in that injecting water during oxidation of carbon monoxide to form carbon dioxide.
11. Method as claimed in claim 10, wherein the water is injected in vapour form or
aerosol form.
12. Method as claimed in claim 10 or 11, comprising the step of : supplying
compressed air to a process gas between the oxidation of carbon monoxide and the
fuel cell unit and/or to a cathode of the fuel cell unit.
13. Method as claimed in any one of the claims 10 to 12, comprising the step of: separating water from an exhaust gas flow from a cathode of the fuel cell unit and/or from an exhaust gas flow from an anode of the fuel cell unit and supplying to the reformer process.
14. Method as claimed in any one of the claims 10 to 13, comprising the step of: burning an exhaust gas from an anode of the fuel cell unit and supplying corresponding waste heat to the reformer process.
15. Method as claimed in any one of the claims 10 to 14, comprising the step of:
burning raw material and supplying corresponding heat energy to the reformer
process.
16. Method as claimed in any one of the claims 10 to 15, wherein the raw material
is a substance containing hydrogen, in particular methanol or petrol.



Documents:

575-MAS-1999 FORM-6 01-02-2010.pdf

575-mas-1999-abstract.pdf

575-mas-1999-assignment.pdf

575-mas-1999-claims.pdf

575-mas-1999-correspondence others.pdf

575-mas-1999-correspondence po.pdf

575-mas-1999-description complete.pdf

575-mas-1999-drawings.pdf

575-mas-1999-form 1.pdf

575-mas-1999-form 26.pdf

575-mas-1999-form 3.pdf

575-mas-1999-form 4.pdf

575-mas-1999-form 5.pdf

575-mas-1999-pct.pdf

abs 0575-mas-1999 abstract .jpg


Patent Number 246094
Indian Patent Application Number 575/MAS/1999
PG Journal Number 07/2011
Publication Date 18-Feb-2011
Grant Date 14-Feb-2011
Date of Filing 20-May-1999
Name of Patentee VOLKSWAGEN AKTIENGESELLSCHAFT
Applicant Address D-38436 WOLFSBURG
Inventors:
# Inventor's Name Inventor's Address
1 Dr. OLAF DUBEL TRIFTWEG 4, D-38550 ISENBUTTEL
2 Dr. AXEL KONIG GALGENKAMP 13, D-38448 WOLFSBURG
PCT International Classification Number H01M08/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 19822691.8 1998-05-20 Germany