Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1999-11-17
2001-11-27
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C429S006000
Reexamination Certificate
active
06322916
ABSTRACT:
The present invention relates to a method of operating a molten carbonate fuel cell, which fuel cell comprises a porous anode, a carbonate-comprising matrix and a porous cathode, wherein the anode is supplied with a hydrogenous gas and the cathode is supplied with a oxygenous gas and primary carbon dioxide, the fuel cell is operated at an elevated temperature, with the carbonate of the carbonate-comprising matrix being in a liquid state, oxygen and carbon dioxide are reacted at the cathode, yielding carbonate ions which move from the cathode to the anode generating an electric voltage between the anode and the cathode, and water that has been formed is led away from the fuel cell together with carbon dioxide.
Such a method is well-known in the prior art. In said method hydrogen, often in the form of coal gas (a mixture of predominantly hydrogen and carbon monoxide) or reform gas (a mixture of predominantly hydrogen and carbon dioxide) is supplied to the anode. Hydrogen donates electrons to the anode. The cathode is supplied with a mixture of oxygen and primary carbon dioxide, usually carbon dioxide-enriched air (70% air: 30% CO
2
). The electrons donated by the hydrogen are accepted by the oxygen. Thus electric energy is generated. The overall reaction taking place in the fuel cell (equation 1 of the formula sheet) is purely a reaction between hydrogen and oxygen forming water. However, in a molten carbonate fuel cell, carbon dioxide plays a role as mediator taking care of the oxygen transport in the fuel cell. To this end primary carbon dioxide is supplied to the cathode. The cathode is often made from porous catalyst material such as nickel oxide (NiO). Under the conditions prevailing during the operation of the fuel cell, 650° C., and an environment containing aggressive carbonate ions, said cathode slowly but surely dissolves. The heat capacity of the mixture comprising remaining oxygen and carbon dioxide being led along the cathode is utilized, for instance, by using a turbine to generate additional electric energy. A portion of the mixture is subsequently supplemented with air and primary carbon dioxide and returned to the cathode. To do this, a cost-raising circulation system and a CO
2
-recuperation system is required.
It is the objective of the present invention to provide a method according to the preamble, in which the cathode is better protected against the effect of carbonate ions and the life of the fuel cell is prolonged. In addition, a further objective of the invention is to eliminate the need for a circulation system. Further objectives will become clear from the following description.
SUMMARY OF THE INVENTION
The objectives according to the invention are realized by a method according to the preamble which is characterized in that the carbonate-comprising matrix is provided with a channel and via said channel primary carbon dioxide-comprising gas is introduced into the carbonate-comprising matrix at a distance from the cathode.
By keeping the carbon dioxide supply at a distance from the cathode, the environment near the cathode is a less detrimental one. Moreover, the low CO
2
tension prevailing near the cathode in accordance with the invention, promotes an important partial reaction, as will be explained below, which is favourable for the performance of the fuel cell.
JP 63.248 076 describes a method of preventing gas leakage from a fuel cell by placing said fuel cell in a pressure container. CO
2
gas is used as a pressurizing gas and the pressure in the pressure container is slightly higher than the operating pressure of the stack. Mention is made that CO
2
gas leaked into the stack supplements CO
2
gas consumed at the cathode, decreasing the voltage drop in the cell.
The present invention also relates to a fuel cell of the molten carbonate kind, which fuel cell possesses a porous anode, a porous cathode and a carbonate-comprising matrix placed between the porous anode and the porous cathode, having at the anode side an inlet for a hydrogenous gas and an outlet for reaction products and unused gas and at the cathode side an inlet for oxygenous gas and an outlet for unused gas.
To apply the method according to the invention in a fuel cell of this kind said fuel cell is characterized in that the carbonate-comprising matrix is provided with a channel for the supply of primary carbon dioxide-containing gas and for the distribution of the primary carbon dioxide-containing gas over the carbonate-comprising matrix.
Thus an installation is provided which allows the supply of carbon dioxide in the vicinity of, yet at a distance from the cathode. In addition the installation provides more extensive possibilities for the control of the streams to be supplied, so that the design of the installation may be better suited to the operational conditions in an industrial environment, such as the available fuel stream.
According to a preferred embodiment the supply and distribution channel is provided with an outlet for excess carbon dioxide gas.
An installation of this kind is suitable for the utilization of heat produced by the fuel cell by means of the carbon dioxide-containing gas as cooling agent.
Finally, the present invention relates to a fuel cell stack comprising at least two stacked fuel cells, each fuel cell having inlet openings for the supply of hydrogen to the anode and for the supply of oxygen to the cathode, respectively having discharge openings for non-reacted hydrogen and oxygen and water that has been formed and the inlet openings for hydrogen being aligned to form a supply conduit for hydrogen, the inlet openings for oxygen being aligned to form a supply conduit for oxygen respectively the outlet openings being aligned to form the respective discharge conduits.
A fuel cell stack of this kind is generally known in the art. In said fuel cell stack the cathode and the anode of successive fuel cells are separated by means of a separator plate made, for instance, from stainless steel. By means of such a fuel cell stack a greater capacity can be achieved, respectively connecting the individual fuel cells in series will result in a higher voltage.
According to the invention such a fuel cell stack is characterized in that each fuel cell has an inlet opening for the supply of carbon dioxide and an outlet opening for the discharge of non-reacted carbon dioxide, and the carbon dioxide inlet openings are aligned to form a carbon dioxide supply conduit and the carbon dioxide outlet openings are aligned to form a carbon dioxide discharge conduit.
In this manner a simply constructed fuel cell stack is provided by means of which carbon dioxide can be sup
5
plied to the fuel cell installation.
The invention further relates to a method of generating electricity with the aid of a fuel cell possessing an anode and a cathode, wherein water and a carbonaceous material are heated at a high temperature by means of heat exchange, yielding a hydrogenous gas, the hydrogenous gas is supplied to the anode of the fuel cell and the oxygenous gas is supplied to the cathode of the fuel cell yielding electricity and a hydrogen-depleted gas stream, the hydrogen-depleted gas stream is supplied with an oxygenous gas and the hydrogen-depleted oxygenous gas stream is at least partially oxidized producing heat, which heat is utilized to heat the water and the carbonaceous material by means of heat exchange.
The method according to the invention thus provides a simple method of forming a hydrogenous gas mixture from a fuel which, in itself, is not suitable for the fuel cell. The particular advantage herein is also that the processes for the formation of hydrogen and the generation of electricity take place at substantially the same temperature, while the temperature of the gas stream from the anode needs to be raised only moderately to achieve good heat transfer—preferably taking place in counter-flow—to water and carbonaceous material. The method is at least partially of a self-regulating nature, which simplifies the control of the method and the installation necessary for the applicatio
Dijkema Gerhard Pieter Jan
Hemmes Klaas
Kalafut Stephen
Pitney Hardin Kipp & Szuch LLP
Technische Universiteit Delft
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