Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-08-10
2003-06-03
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S010000, C429S006000, C429S006000
Reexamination Certificate
active
06572996
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high temperature fuel cell generators wherein depleted fuel and depleted air are kept separate from each other to allow treatment of depleted fuel by a special apparatus to separate essentially pure carbon dioxide from depleted fuel.
2. Background Information
Tubular, solid oxide electrolyte fuel cell “SOFC” generators have been well known in the art for almost twenty years, and taught, for example by A. O. Isenberg in U.S. Pat. No. 4,395,468. There, in the main embodiment, air, as oxidant, reacted at the inside “air” electrode of a closed tubular SOFC, to yield depleted air; and fuel, such as CO and H
2
, reacted at an outside “fuel” electrode of the closed tubular SOFC to yield depleted fuel, all in a “generating chamber,” at high temperatures (for example, about 1000° C.). The air electrode generally comprised a doped lanthanum manganite, the fuel electrode generally comprised a nickel cermet and an electrolyte disposed between the electrodes generally comprised a stabilized zirconia. The depleted fuel was subsequently completely combusted with the depleted air in a separate combustion chamber, to preheat feed air. This basic SOFC generator design was carried forward, with other improvements, as shown for example in U.S. Pat. Nos.: 4,664,986; 5,573,867; and 5,733,675 (Draper et al.; Zafred et al. and Dederer et al.). Other designs have used a series of fuel cell stacks, each providing a stage containing a different electrolyte operating at a lower temperature to improve fuel gas utilization, as taught in U.S. Pat. No. 5,712,055 (Khandkar). In a somewhat similar fashion, in one embodiment of U.S. Pat. No. 5,134,043 (Nakagawa), “depleted fuel” from a first molten carbonate fuel cell system was sent to a separate molten carbonate anode, where the product was then mixed/contacted with oxidant/air before being introduced into the cathode section of the first molten carbonate electrolyte fuel cell. While tubular fuel cells are emphasized herein, flat/planar fuel cells, which are well known in the art, may also be used.
However, such designs could release byproducts of combustion, such as carbon dioxide into the atmosphere. Efforts are now being made on an international level to globally reduce the release of so-called “green house gasses” which includes carbon dioxide, which may contribute to global atmospheric warming. Such efforts may, indeed, lead to future legislation regarding carbon dioxide emissions from SOFC's. What is needed is a means to further treat the spent fuel from fuel cell generators to not only reduce or eliminate carbon dioxide emissions but also to increase the capacity of the fuel cell generators to further utilize feed fuel. Such a need applies to both tubular and flat plate type fuel cells.
In the area of reducing carbon dioxide emissions from power plants utilizing a variety of types of fuel cells, in order to reduce the “green house effect”, U.S. Pat. No. 4,751,151 (Healy et al.) taught a carbon dioxide absorber, such as monoethanolamine, included as a regenerable carbon dioxide absorbent, for stripping carbon dioxide, followed by subsequent cooling and compression. U.S. Pat. No. 5,064,733 (Krist et al.), recognizing prior art conversion of natural gas into DC electricity plus carbon dioxide and water-with the accompanying creation of a DC electrical power-in a solid oxide fuel cell taught conversion of the carbon dioxide and water to C
2
H
4
, C
2
H
6
and C
2
H
2
by use of a copper, copper alloy or perovskite cathode. That cathode was in contact with the CO
2
, and H
2
O and a dual layered anode made of metal oxide perovskite next to the electrode with an outer contacting layer of rare earth metal oxide contacting CH
4
. This provided for concurrent gas phase electrocatalytic oxidative dimerization of methane at an anode on one side of a solid electrolyte and reduction of carbon dioxide to gaseous hydrocarbons at a cathode on the other side of the solid electrolyte. Other CO
2
treatments include U.S. Pat. No. 5,928,806 (Olah et al.), where a regenerative fuel cell system containing two electrochemical cells in fluid communication were taught, one cell oxidizing an oxygenated hydrocarbon, such as methyl alcohol, formic acid, etc., to CO
2
and H
2
O and a second cell reducing CO
2
and H
2
O to an oxygenated hydrocarbon. This produced methyl alcohol and related compounds directly from CO
2
. Also, U.S. Pat. No. 5,866,090, (Nakagawa et al.) taught reacting carbon dioxide containing exhaust, from a power plant which uses fuel cells, with a composition containing lithium zirconate at approximately 450° C., so that the carbon dioxide reacts with the lithium zirconate to produce lithium carbonate and zirconia. The lithium carbonate and zirconia are then subjected to a temperature of 600° C. or more, so as to produce lithium zirconate and pure carbon dioxide.
While a great many methods to treat carbon dioxide are known, a new fuel cell generator design is needed to allow segregation and further concentration of the carbon dioxide for such treatment.
SUMMARY OF THE INVENTION
Therefore it is a main object of this invention to provide an improved fuel cell generator design, allowing segregation of carbon dioxide generated at the fuel electrodes by an integrated secondary fuel reactor means.
It is a further object of this invention to provide an improved generator design allowing ultra high fuel utilization capacity by use of an integrated secondary fuel reactor means.
These and other objects are accomplished by providing a high temperature fuel cell generator comprising a separate generator chamber containing tubular solid oxide electrolyte fuel cells which operate on oxidant and fuel to yield depleted oxidant and depleted fuel, and a separate fuel reactor chamber containing a depleted fuel reactor-selected from a fuel cell and an electrolysis cell, and potentially operating at a different temperature than the generator chamber-where all oxidant and fuel passages are separated and do not communicate directly with each other, so that fuel and oxidant remain effectively separated, where a depleted fuel exit is provided in the separate fuel reactor chamber for exiting a gas consisting essentially of carbon dioxide and water for further treatment, and where depleted oxidant exits are provided to exhaust to the environment.
The invention also comprises a high temperature fuel cell generator, comprising: a housing defining and separating a generator chamber; a separate fuel reactor chamber; a depleted oxidant discharge chamber; a plurality of fuel cells, each having an electrolyte contacted on one side by an air electrode and on the other side by a fuel electrode, said fuel cells disposed within the generator chamber; means to react substantially all of the fuel, said means selected from oxidant-fed fuel cells and steam-fed electrolysis cells disposed in the separate fuel reactor chamber; means to flow a feed fuel gas to contact the fuel electrode of fuel cells in the generator chamber, where said fuel can react and provide partially depleted fuel gas; means to flow a feed oxidant gas to contact the air electrode of fuel cells in the generator chamber, where said oxidant can react and provide a depleted oxidant gas; means to flow a second feed oxidant gas to the separate fuel reactor chamber, where the means to react substantially all of the fuel is a fuel cell, or means to flow steam to the separate fuel reactor chamber, where the means to react substantially all of the fuel is an electrolysis cell; and means to flow partially depleted fuel gas from the generator chamber to contact the outside of the means to react substantially all of the fuel in the separate fuel reactor chamber, where said depleted fuel can further react and provide a completely depleted fuel gas consisting essentially of carbon dioxide and water, where depleted oxidant gases are kept separated from all depleted fuel gases and said depleted oxidant gases flow into a separate depleted oxidant discharge ch
Gopalan Srikanth
Isenberg Arnold O.
Veyo Stephen E.
Maples John S.
Siemens Westinghouse Power Corporation
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