Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1999-12-13
2001-12-04
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000
Reexamination Certificate
active
06326095
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates in general to solid oxide fuel cells, and in particular, to a new and useful integrated manifold/reformer for solid oxide fuel cells.
Fuel cells are widely recognized as one of the most promising technologies to meet future power generation requirements, particularly for distributed power applications. Of the various fuel cells under development, planar Solid Oxide Fuel Cells (SOFCs) are particularly attractive because of their solid state construction (no liquid electrolyte). The ability to be integrated into compact, rugged power systems fueled with readily available fossil fuels is also an important advantage. The development and commercialization of planar SOFC technology requires innovative approaches to system design that allow integration into compact power systems.
FIG. 1
illustrates the component arrangement used in a known SOFC system of a nominal 1 kilowatt (kW) size. Before operation, a refractory-insulated hood (not shown) is lowered over the equipment, forming a hot chamber
100
. The components normally operate at about 850° C. Of interest here are the flow of the fuel gas through the system and the energy transfers between the fuel cells in fuel cell stack
102
, reformer
104
, and chamber
100
. Typical values from that known design are used in the following description for quantification.
Natural gas is a popular choice for fuel. For a 2-kilowatt size, about 1 pound/hr of natural gas is mixed with about 2.2 pounds/hr of steam to form the fuel gas
108
. This mixture flows up from an insulated base plate
106
, as shown, into the reformer
104
. The reformer
104
is typically filled with a steam reforming catalyst made from a nickel metal base. The catalyst changes the composition of the gas by way of certain chemical reactions. The chemical reactions taking place in the reformer
104
are endothermic so the reformer
104
absorbs about 2.4 kilowatts of heat from the components in the hot chamber
100
. The fuel gas flowing out of the reformer
104
at
108
is at about 790 EC and includes about 1.1 pound/hr of steam, 1.7 pounds/hr of carbon monoxide, and 0.4 pound/hr of hydrogen.
The reformed fuel flows out the top of the reformer through an insulated tube
110
to the inlet fuel manifold
112
. The manifold seals around the perimeter of the fuel cell stack
102
and forces the fuel gas to flow through channels in the stack interconnects (right to left). The manifold also acts as a plenum to supply the fuel gas evenly to the fuel cells. The fuel cell stack
102
is also supplied with air, which flows from back to front in FIG.
1
. The fuel cell stacks use about 60% of the energy in the fuel gas to produce 2 kilowatts of electric power. In this process, about 3.9 kilowatts of heat is released in the stacks. This heat is removed from the stacks in two ways. One way is to transfer heat to the airflow. The other way is to transfer heat to other components in the chamber, primarily by radiation. Since the fuel cell stacks are generating excess heat and the reformer requires heat input, the stacks are relatively hotter than the reformer. Consequently, the reformer draws heat from the stacks, preferentially from stacks, or stack surfaces that are near to it.
The partially used fuel gas leaving the fuel cell stacks is gathered in the outlet fuel manifold
114
and exhausts through a tube
116
as shown. At this point, any unused fuel burns in a flame as it enters the hot chamber.
SUMMARY OF THE INVENTION
The present invention is a new fuel inlet manifold that performs all the functions of the prior manifold, as well as the functions of the reformer, which results in a compact power system.
The compactness of a fuel cell power system is very important from a commercial standpoint. In addition to how much room is needed for an installation, indirect effects on system costs due to size and system heat losses are important. The present invention allows a significant reduction in size. This can be seen easily by referring to FIG.
1
. By roughly doubling the thickness of the inlet fuel manifold shown, the reformer and tubing connecting it to the manifold is eliminated according to the present invention. The size of the insulated base and hood can be significantly reduced.
Another advantage is that the fuel gas plumbing is simpler. According to the invention the mixture of natural gas and steam flows directly into the manifold rather than into the reformer.
The relatively large amount of heat absorbed from the hot chamber by the reformer presents a significant design problem. In larger systems (2-kilowatts or more), multiple fuel cell stacks are needed to produce the electric power. In the prior art, the reforming process would be done in one reformer. However, the reformer is a heat sink that draws heat unevenly from the chamber and stacks. Stacks located closer to the reformer lose more heat and tend to operate at a lower temperature. This unbalances power production by the stacks and can affect stack life. This problem is eliminated with this invention. Each stack has its own, identical reformer located in the inlet fuel manifold. Consequently, every stack sees the same environment and stack temperatures are balanced.
In the prior art, the reformer absorbed heat by direct thermal radiation from the stacks and also from the hot chamber, either by radiation from other components or by convection from the gas inside the chamber. Controlling the relative amounts of heat is usually desirable in the design process yet is very difficult due to the complex heat transfer mechanisms and geometry of the components in the chamber. For example, it is usually desirable to remove as much heat directly from the stacks as possible because this lessens the requirement for airflow. Less airflow means smaller blowers, less exhaust heat loss, etc. The integrated manifold/reformer also absorbs heat from both the fuel cell stack and the chamber. However, the relative amounts can be easily controlled in the design process through the placement of insulation outside or inside the manifold according to this invention.
The integrated manifold/reformer also allows for a customized heat input distribution from the stack bottom to top. In this way, the heat sink seen by the stack can be adjusted to account for heat losses out the top and bottom of the stack to give a uniform vertical stack temperature profile.
Accordingly another object of the present invention is to provide a fuel cell manifold arrangement, comprising a fuel cell stack having a fuel gas inlet side and a fuel gas outlet side; a manifold enclosure connected to and sealed to the inlet side of the fuel cell stack and defining with the stack a gas plenum for receiving a fuel gas for inlet into the inlet side of the fuel cell stack; catalyst screen means connected to the manifold enclosure for defining a gas passage for passing fuel gas and for containing a catalyst; a fuel gas catalyst in the manifold enclosure and bounded by the screen means; the manifold enclosure having a gas inlet for receiving fuel gas, the gas inlet communicating with the screen means for passing fuel gas through the screen means and past the catalyst in the gas passage; plate means in the manifold enclosure for separating the catalyst from the plenum; heat insulation on at least part of the manifold enclosure and on at least part of the plate means for insulating the manifold enclosure from the fuel cell stack and from an exterior of the manifold enclosure; and passage means in the manifold enclosure for defining a passage from the screen means to the plenum for passing fuel gas from the catalyst to the plenum.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which the preferred embodiment of the
Baraona R. C.
Kalafut Stephen
Marich Eric
Sofco L.P.
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