Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2001-08-16
2003-11-18
Gulakowski, Randy (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C429S010000
Reexamination Certificate
active
06649292
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a fuel cell system having a reformer unit for generating a reformate which is provided as fuel for a fuel cell unit. The system further includes a sensor for monitoring the reformate quality and a valve which can be driven in dependence upon the sensor.
BACKGROUND OF THE INVENTION
Fuel cell technology gains ever more in significance especially in connection with future drive concepts of vehicles.
Fuel cells offer the possibility of converting chemically bonded energy directly into electrical energy which can be subsequently converted into mechanical drive energy with the aid of an electric motor. In contrast to thermal power engines, the efficiency of a fuel cell is not limited by the Carnot efficiency. Present day preferred fuel cells consume hydrogen and oxygen and convert these elements into the environmentally friendly end product, namely, water.
Because of the technical problems in the storage of hydrogen in vehicles, development has gone over to generate the hydrogen, as required, via a so-called reformation or partial oxidation of hydrocarbons. Hydrocarbons of this kind are present in the form of conventional fuels such as gasoline, diesel oil or natural gas; however, other hydrocarbons could also be used for this purpose, such as methane or methanol.
In conventional fuel cell systems, so-called PEM fuel cells are often used which, however, react especially to carbon monoxide components in the hydrogen-rich medium with adsorbed CO on the catalytic cathode so that the conversion of hydrogen at the electrode is made more difficult or is prevented. This CO-binding is referred to by experts generally with the term “poisoning” of the cathode. For this reason, fuel cell systems have to ensure the production of a substantially carbon monoxide free hydrogen-rich medium.
Accordingly, the carbon monoxide component in the hydrogen-rich reformate is almost completely reduced with the aid of reactors. In a first step, a reactor unit is connected downstream of the reformer and this reactor unit oxidizes the carbon monoxide to CO
2
while adding water via a so-called shift reaction whereupon hydrogen is, in turn, released. The carbon monoxide results from the conversion of the fuel. However, residual quantities of carbon monoxide remain contained in the reformate gas at a concentration which still leads to a non-tolerable poisoning of the fuel cell.
Reactor units are used to convert the residual carbon monoxide quantities which are still present. These reactor units, for example, almost completely reduce the residual carbon monoxide quantities by means of catalytic oxidation of the carbon monoxide while adding oxygen at a suitable oxidation catalytic converter. To reduce the carbon monoxide component to values less than 50 ppm, preferably multi-stage carbon monoxide oxidation units are utilized and oxygen is supplied, for examples, separately to each stage. The oxygen is often metered in the form of air oxygen.
In fuel cell systems, for example, short-term operating disturbances occur at the present time in the reformer as well as in the reaction unit connected downstream so that, for example, the CO concentration at the input of the fuel cell system exceeds a threshold value which sometimes leads to a comparatively long poisoning of the fuel cell. For this reason, gas sensors have been provided up to now which are mounted between the individual reactor units, that is, ahead of the fuel cell unit. A monitoring of the state of the reformate is made possible by these gas sensors and, with the aid of a suitable control apparatus, the control of the chemical processing of the fuel cell system is possible. The requirements placed on the gas sensors and their operation including their preferred arrangement in the fuel cell system are described, for example, in U.S. Pat. No. 6,083,637 which is incorporated herein by reference.
Also in U.S. Pat. No. 6,083,637, an arrangement is described which switches a valve in dependence upon the signals of the gas sensors so that the reformate having unsuitable quality is guided past the fuel cell unit. If possible operational disturbances occur in the reformer, that is, in the reactor units (that is, during the preparation of the reformate), the poisoning of the fuel cell unit is hereby prevented. However, it is disadvantageous that the supply of the fuel cell unit comes to a stop in the case of detouring the reformate, that is, the fuel. As a consequence, the electric output power of the fuel cell unit reduces sharply after a short time.
SUMMARY OF THE INVENTION
In contrast to the above, it is an object of the invention to provide a fuel cell system of the above kind which reacts very rapidly to disturbances during the preparation of the reformate. The fuel cell system especially prevents that disturbances lead to damage of the fuel cell unit and the electric output power of the fuel cell unit continues to be controllable.
The fuel cell system of the invention includes: a fuel cell unit; a reformer unit for generating a reformate as a fuel for the fuel cell unit; sensor means for monitoring the quality of the reformate; a storage unit for holding fuel which can be fed to the fuel cell; valve means for connecting the storage unit to the fuel cell unit so as to permit fuel contained in the storage unit to be fed to the fuel cell unit in dependence upon the quality of the reformate; and, control means for driving the valve means in dependence upon the sensor means.
The fuel cell system according to the invention incorporates the feature that at least one storage unit is provided for supplying fuel to the fuel cell unit in dependence upon the quality of the reformate.
Fuel of unsuitable quality (that is, when the reformate quality, for example, drops below a defined threshold value), can, in this way, be guided past the fuel cell unit in an advantageous manner while, at the same time, the supply of fuel of suitable quality to the fuel cell unit can be realized. In this way, the storage unit of the fuel cell system of the invention ensures that damage to the fuel cell unit by fuel of unsuitable quality is prevented and that the supply and therefore the electrical output power of the fuel cell unit can still be controlled. For example, the supply of fuel from the storage unit can be adjusted in dependence upon the configuration of the fuel cell so that the output power of the fuel cell unit does not drop off.
Preferably, the storage unit is so dimensioned that it bridges the duration until the reestablishment of the proper reformate quality. Alternatively hereto, and in a further embodiment of the invention, the storage unit or several storage units are at least so dimensioned that a proper running down, that is, a bringing of the entire fuel cell system to standstill can be realized. Especially generously held storage units or times are, for example, advantageous for traction applications such as an automobile, railroad, bicycle with ancillary engine, ship, aircraft or the like.
If the fuel cell system is one wherein disturbances occur rarely and/or for only a short time (that is, for example, in time durations of one or several months or only for fractions of seconds), then the use of an irreversible fuel storage is advantageous. If required, charged metal hydride stores or devices can be used which release fuel via a chemically irreversible process. Inter alia, the conversion of water with suitable metal hydrides is realizable as is the action of acids on suitable non-noble metals or the like.
A further embodiment of the invention is the additional or alternative use of a reversible store. For this purpose, a pressure store or the like is, for example, usable. Present day fuel cell systems exhibit comparatively short disturbances which occur regularly. These short disturbances can, for example, at least be compensated by means of a reversible storage unit. The combination of at least one reversible storage unit and an irreversible storage unit is especially advantageous when the duration of running down the
Breuer Norbert
Schiller Christian
Gulakowski Randy
Ottesen Walter
Robert & Bosch GmbH
Scaltrito Donald V.
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