Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-08-18
2002-09-03
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000
Reexamination Certificate
active
06444342
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to oxidant feed tube supports for tubular solid oxide fuel cells (SOFCs) disposed in a fuel cell generator.
2. Background Information
High temperature, solid oxide electrolyte fuel cell generators, which are made of mostly ceramic components, and which allow controlled leakage among plural chambers in a sealed housing, are well known in the art, and are taught in U.S. Patent Nos. 4,395,468 and 5,573,867 (Isenberg and Zafred, et al., respectively). One type of such prior art generator design
12
is shown in
FIG. 1
of the present application (which corresponds to
FIG. 4
of the Zafred et al. patent). Here, oxidant gas enters air manifold
48
through oxidant inlet lines
20
as oxidant stream
50
(usually air), passing upward, possibly through cooling ducts, to a top air distribution plenum
52
. The oxidant stream
50
′ is then transferred and passes downward via individual thin, ceramic oxidant feed tubes
51
. The oxidant passes down the feed tubes
51
into the bottom interior of each fuel cell
36
, where, as is well known in the art, the oxidant reverses flow and passes up the annular space between the oxidant feed tube and the interior air electrode, where it reacts along the air electrode interior surface. The reacted oxidant, in one embodiment of the fuel cell generator, finally enters a combustion chamber section
54
as spent oxidant, where the spent oxidant then combusts with spent fuel and the remaining unreacted feed fuel, to provide exhaust gas
56
, which flows to an exhaust manifold. Part of the spent fuel may also be recirculated to the ejector
40
, as shown in FIG.
1
. The exhaust gas
56
passes through exhaust ducts
58
. A power lead
84
is also shown in
FIG. 1
, and fuel inlet is shown as piping
38
which passes through prereformer
42
.
The tubular fuel cells include a solid oxide electrolyte sandwiched between two porous ceramic electrodes, an outer fuel electrode and an inner air electrode.
FIG. 2
of the present application shows a prior art oxidant/air feed tube conduit support system employed in the Isenberg patent (shown in
FIG. 2
of Isenberg). A metal tube sheet
34
has associated bores
60
that fit loosely around the oxidant feed tube conduits
51
to allow free thermal expansion. The oxidant feed tube conduits
51
are comprised of alumina or alumina compounds, and the tube sheet is covered with an insulation
62
such as low density alumina. Leakage of oxidant, into the combustion (pre-heating) chamber
16
, as indicated by arrow
63
in
FIG. 2
, was considered acceptable. The oxidant feed tubes then proceed into the interior of the tubular fuel cells, as shown in
FIG. 1
of the present application.
A later oxidant/air feed tube conduit support system was taught by Draper et al., in U.S. Pat. No. 4,664,986, and also in U.S. Pat. Nos. 4,808,491 and 4,876,163 (both Reichner). The prior art system of Draper et al. taught welding the air feed tube conduits to associated subheader tubes, so that there was substantially no air leakage. In the prior art Reichner system, as shown in
FIG. 3
of the present application (and
FIG. 1B
of the Reichner '491 patent), oxidant/air feed
50
flows into top oxidant/air distribution plenum
52
and then into further oxidant/air distribution plenums
52
′, where the oxidant/air then passes downward via individual oxidant feed tubes
51
. At the top of the oxidant feed tubes
51
spherical supports
70
kept the oxidant feed tubes in place. These spherical supports required a machined spherical seat
72
in the Inconel plenum wall
74
at the bottom of the plenums
52
′. Insulation
76
surrounds the plenums. Steel enclosure
78
surrounds the fuel cell generator. Exhaust gas passages are shown as channels
80
and the bottom lower plenum enclosure insulation board is shown as
82
supporting the bottom of plenum
52
′. The Isenberg design (as shown in
FIG. 2
of this application) required precise cutting of the insulation layer and after thermal cycling, the possibility that the air feed tube would slip out of place to contact the bottom of the fuel cell cutting off the air supply for that cell. The Draper et al. design was very expensive and very heavy and required major machining and welding of Inconel components. The Reichner design (shown as
FIG. 3
of the present application) also required substantial machining to properly set the spherical support. Also, in current SOFC design, a perfectly centered 72 in. (182.8 cm) long air feed tube in a 66 in. (167.6 cm) long cell permits only 0.1° freedom of movement before it closes the 0.125 inch (0.32 cm) radial gap and hits the inside surface of the cell. This radial gap is further reduced if there is any bow in the cell or the air feed tube. The difficulty of assembling the air feed tube in a cell is further compounded by any cell-to-cell and bundle-to-bundle lateral and torsional misalignment resulting from corresponding sintering operations. Due to the lack of lateral freedom and the extremely limited angular movement of the air feed tubs, there is a great likelihood of wedging the air feed tube into the cell wall during assembly if there is any distortion (lateral, torsional, or bow) of the cell.
What is needed is an improved, simpler, less expensive oxidant/air feed tube conduit support system that will require only minimal or no metal finishing. Therefore, it is one of the main objects of this invention to support the oxidant/air feed tubes in such a way as to keep them from contacting the sides or bottom inside of the fuel cells. It is another main object to provide a simpler, significantly less expensive oxidant/air feed tube support system which requires minimal or no metal finishing. It is also an object of this invention to provide a minimum leakage seal between the air plenum and the rest of the SOFC module and to bring the design to a commercialization level.
SUMMARY OF THE INVENTION
These and other objects of the invention are accomplished by providing a solid oxide fuel cell generator comprising: hollow, tubular fuel cells with interior air electrodes; an oxidant plenum having a lower enclosing member; and oxidant feed tubes; where the enclosing member contains a plurality of holes, and supports the oxidant feed tubes, which pass from the oxidant plenum into the center of the fuel cells through the holes in the enclosing member; and where a compliant gasket around the top portion of the oxidant feed tubes and on top of the enclosing member helps center the oxidant feed tubes within the fuel cells. The compliant gasket provides a cushion during shipping and during generator use. The gasket is held on by friction, no glue being necessary.
The invention also resides in a solid oxide fuel cell generator comprising: (1) a plurality of electrically connected hollow, tubular, solid oxide fuel cells which can operate on feed fuel and oxidant gases; (2) an oxidant plenum within the generator for receiving and distributing fed oxidant to the fuel cells; (3) a lower enclosure for the oxidant plenum having a plurality of holes therethrough; and (4) a plurality of hollow oxidant feed tubes extending from the oxidant plenum, through the lower oxidant plenum enclosure holes into the inside of the fuel cells where the lower oxidant plenum enclosure has at least a flat top surface facing the oxidant plenum and supports the oxidant feed tubes by contact with a washer and gasket tube support combination, which combination is disposed around the outer circumference of the oxidant feed tubes and on top of the flat top surface of the oxidant plenum enclosure;. where the tube support combination consists of a top, hard washer bonded to the oxidant feed tubes and a compliant gasket disposed on top of and contacting the flat top surface of the lower oxidant plenum enclosure between the washer and the lower oxidant plenum enclosure, and where at least the gasket has a bottom surface which mates to the flat top surface of the lower oxidant plenu
Doshi Vinod B.
Hager Charles A.
Ruka Roswell J.
Kalafut Stephen
Siemens Westinghouse Power Corporation
Yuan Dah-Wei
LandOfFree
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