U.S. patent application number 09/988840 was filed with the patent office on 2002-08-01 for thermally enhanced compact reformer.
This patent application is currently assigned to Ztek Corporation. Invention is credited to Hoag, Ethan D., Hsu, Michael S..
Application Number | 20020102188 09/988840 |
Document ID | / |
Family ID | 24531182 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020102188 |
Kind Code |
A1 |
Hsu, Michael S. ; et
al. |
August 1, 2002 |
Thermally enhanced compact reformer
Abstract
A natural gas reformer comprising a stack of thermally
conducting plates interspersed with catalyst plates and provided
with internal or external manifolds for reactants. The catalyst
plate is in intimate thermal contact with the conducting plates so
that its temperature closely tracks the temperature of the
thermally conducting plate, which can be designed to attain a near
isothermal state in-plane to the plate. One or more catalysts may
be used, distributed along the flow direction, in-plane to the
thermally conducting plate, in a variety of optional embodiments.
The reformer may be operated as a steam reformer or as a partial
oxidation reformer. When operated as a steam reformer, thermal
energy for the (endothermic) steam reforming reaction is provided
externally by radiation and/or conduction to the thermally
conducting plates. This produces carbon monoxide, hydrogen, steam
and carbon dioxide. When operated as a partial oxidation reformer,
a fraction of the natural gas is oxidized assisted by the presence
of a combustion catalyst and reforming catalyst. This produces
carbon monoxide, hydrogen, steam and carbon dioxide. Because of the
intimate thermal contact between the catalyst plate and the
conducting plates, no excessive temperature can develop within the
stack assembly. Details of the plate design may be varied to
accommodate a variety of manifolding embodiments providing one or
more inlets and exit ports for introducing, pre-heating and exhaust
the reactants.
Inventors: |
Hsu, Michael S.; (Lincoln,
MA) ; Hoag, Ethan D.; (East Boston, MA) |
Correspondence
Address: |
LAHIVE & COCKFIELD
28 STATE STREET
BOSTON
MA
02109
US
|
Assignee: |
Ztek Corporation
|
Family ID: |
24531182 |
Appl. No.: |
09/988840 |
Filed: |
November 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09988840 |
Nov 19, 2001 |
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09712020 |
Nov 14, 2000 |
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09712020 |
Nov 14, 2000 |
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09459403 |
Jan 11, 1999 |
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6183703 |
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09459403 |
Jan 11, 1999 |
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08631432 |
Apr 12, 1996 |
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5858314 |
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Current U.S.
Class: |
422/168 ;
422/173; 422/198; 422/600 |
Current CPC
Class: |
Y02P 20/129 20151101;
H01M 8/2484 20160201; C01B 2203/80 20130101; C01B 2203/1205
20130101; H01M 8/2404 20160201; B01J 12/007 20130101; B01J 15/005
20130101; B01J 2219/2485 20130101; C01B 3/382 20130101; C01B
2203/066 20130101; H01M 8/04022 20130101; H01M 8/0631 20130101;
C01B 2203/0866 20130101; C01B 2203/0844 20130101; H01M 8/0618
20130101; B01J 12/005 20130101; C01B 2203/0838 20130101; C01B
2203/1276 20130101; B01J 35/04 20130101; B01J 2219/2493 20130101;
B01D 53/8653 20130101; C01B 2203/82 20130101; H01M 2300/0077
20130101; B01J 2219/2465 20130101; H01M 8/0625 20130101; C01B
2203/0833 20130101; C01B 2203/1035 20130101; B01J 2219/2458
20130101; B01J 2219/2477 20130101; C01B 2203/142 20130101; H01M
8/0662 20130101; Y02P 20/52 20151101; B01J 19/249 20130101; B01J
2219/2467 20130101; H01M 8/2432 20160201; C01B 2203/0261 20130101;
Y02E 60/50 20130101; B01J 2219/2479 20130101; B01J 2219/2487
20130101; B01D 53/864 20130101; B01J 2208/00309 20130101; H01M
8/0612 20130101; C01B 2203/0244 20130101; C01B 2203/0811 20130101;
C01B 2203/1041 20130101; C01B 2203/0238 20130101; C01B 2203/1241
20130101; B01J 2219/2453 20130101; B01J 2208/022 20130101; C01B
3/384 20130101; C01B 3/386 20130101; H01M 2008/1293 20130101; B01J
2219/2482 20130101; C01B 2203/0233 20130101; C01B 2203/0283
20130101; H01M 8/2483 20160201; B01J 2219/2498 20130101 |
Class at
Publication: |
422/168 ;
422/188; 422/198; 422/173 |
International
Class: |
B01D 053/34; F01N
003/10; F28D 001/03 |
Claims
Having described the invention, what is claimed is:
1. A plate-type reformer for reforming a reactant into reaction
species during operation, said reformer comprising: a plurality of
catalyst plates having associated therewith one or more catalyst
materials for promoting reformation and a plurality of conductive
plates formed of a thermally conducting material, said catalyst
plates and said conductive plates being alternately stacked to form
a reforming structure, the conductive plates conductively
transferring heat energy in-plane to support the reforming
process.
2. The reformer of claim 1 wherein said reforming process includes
one or more reforming reactions, said reforming reactions including
a catalytically assisted chemical reaction between two or more
reaction species, and a catalytically assisted thermal dissociation
of a single species.
3. The reformer of claim 1 wherein said reforming structure
includes at least one axial manifold for introducing the reactant
thereto and at least one manifold for allowing the reaction species
to exit from the reforming structure.
4. The reformer of claim 1 wherein said reforming structure has an
exposed peripheral surface for exchanging heat energy with an
external environment.
5. The reformer of claim 1 wherein said reforming structure
includes at least one axial reactant manifold for introducing the
reactant thereto and peripheral exhaust means for exhausting the
reaction species from a peripheral portion of the reforming
structure.
6. The reformer of claim 1 further comprising a thermally
conductive, gas-tight housing disposed about the stacked reforming
structure to form a peripheral axial manifold, and means for
allowing the reaction species to enter the peripheral axial
manifold, wherein the reaction species is captured by the gas-tight
housing.
7. The reformer of claim 1 further including a thermally
conductive, gas-tight housing having means for exchanging heat
energy with the external environment and said conductive plate by
one of radiation, conduction and convection.
8. The reformer of claim 1 wherein an outer surface of the
reforming structure contacts an inner surface of a gas-tight
housing, said gas-tight housing being capable of conductively
transferring heat energy to the conductive plates.
9. The reformer of claim 1 further comprising a gas-tight enclosure
of cylindrical configuration for permitting pressurized reformer
operation.
10. The reformer of claim 1 wherein the conductive plate includes
means for providing a generally isothermal condition, in plane of
the conductive plate.
11. The reformer of claim 1 wherein said reforming structure
includes at least one axial reactant manifold for introducing the
reactant thereto, and wherein the conductive plates includes
extension means integrally formed thereon and extending into the
axial reactant manifold for preheating an incoming reactant.
12. The reformer of claim 1 wherein at least one of the conductive
plate and the catalyst plate includes an in-plane surface having
passage means for allowing the reactant to flow over the surface of
the plate.
13. The reformer of claim 1 further including an axial manifold
formed within the reforming structure, passage means formed between
the conductive plate and the catalyst plate, and means for
generating a reactant flow pressure drop through the passage means
between the conductive plate and the catalyst plate that is
substantially greater than the reactant flow pressure drop within
the axial manifold.
14. The reformer of claim 1 further including passage means formed
between the catalyst and conductive plates for allowing an incoming
reactant to pass over a surface of one of the plates, said passage
means maintaining a substantially uniform pressure drop to provide
for a substantially uniform flow of reactants along an axis of the
reforming structure.
15. The reformer of claim 1 further including means for producing a
substantially uniform temperature condition along an axis of the
reforming structure.
16. The reformer of claim 1 wherein the catalyst plate is formed of
a porous catalyst material, the porous material forming passage
means for allowing an incoming reactant to pass through at least a
portion of the plate.
17. The reformer of claim 1 wherein the thermally conductive plate
is formed of a porous conductive material, the porous material
forming passage means for allowing an incoming reactant to pass
through the plate.
18. The reformer of claim 1 wherein the conductive plate is
composed of at least one of a nonmetal such as silicon carbide, and
a composite material.
19. The reformer of claim 1 wherein the conductive plate is
composed of at least one metal such as aluminum, copper, iron,
steel alloys, nickel, nickel alloys, chromium, chromium alloys,
platinum, and platinum alloys.
20. The reformer of claim 1 wherein the catalyst plate is composed
of a ceramic support plate having the catalyst material
coating.
21. The reformer of claim 1 wherein the catalyst material is
selected from the group consisting of platinum, palladium, nickel,
nickel oxide, iron, iron oxide, chromium, chromium oxide, cobalt,
cobalt oxide, copper, copper oxide, zinc, zinc oxide, molybdenum,
molybdenum oxide, and other suitable transition metals and their
oxides.
22. The reformer of claim 1 wherein the catalyst plate is composed
of at least one of platinum, nickel, nickel oxide, chromium and
chromium oxide.
23. The reformer of claim 1 wherein the reactant includes a
hydrocarbon species, and at least one of O.sub.2, H.sub.2O and
CO.sub.2.
24. The reformer of claim 1 wherein the reactant includes at least
one of an alkane, a hydroxyl, a hydrocarbon bonded with a carboxyl,
a hydrocarbon bonded with a carbonyl, an olifin hydrocarbon, a
hydrocarbon bonded with an ether, a hydrocarbon bonded with an
ester, a hydrocarbon bonded with an amine, a hydrocarbon bonded
with an aromatic derivative, and a hydrocarbon bonded with another
organo-derivative.
25. The reformer of claim 1 further including means for coupling
the reaction species exiting the reformer to an external fuel
cell.
26. The reformer of claim 23 wherein the hydrocarbon fuel and at
least one of H.sub.2O and CO.sub.2 undergo an endothermic catalytic
reformation to produce H.sub.2, CO, H.sub.2O and CO.sub.2, the
energy requirements for the endothermic reforming being supplied by
energy produced by an external fuel cell, said energy being
transferred from the fuel cell by the conducting plate through
in-plane thermal conduction.
27. The reformer of claim 23 wherein the hydrocarbon fuel and
O.sub.2 undergo catalytic combustion and reformation to produce
H.sub.2, CO, H.sub.2O and CO.sub.2, and at least one of an
exothermic combustion and an exothermic reaction of an external
fuel cell supplementing the energy requirements for the endothermic
reforming through the in-plane thermal conduction of the conducting
plate.
28. The reformer of claim 23 or 24 wherein the CO and H.sub.2O
undergo catalytic shift reaction to form CO.sub.2 and H.sub.2.
29. The reformer of claim 1 wherein the reforming structure has a
substantially cylindrical shape.
30. The reformer of claim 1 wherein the reforming structure is
cylindrical and at least one of the catalyst plate and the
conductive plate has a diameter between about 1 inch and about 20
inches, and has a thickness between about 0.002 inch and about 0.2
inch.
31. The reformer of claim 1 wherein the reforming structure has a
substantially rectangular shape.
32. A reformer for reforming a reactant into reaction species
during operation, said reformer comprising: a porous and thermally
conductive material interspersed with one or more catalyst
materials to form a reforming structure, the thermally conductive
material transferring heat energy to support the reforming
process.
33. A plate-type reformer for reforming a reactant into reaction
species during operation, said reformer comprising: a plurality of
plates composed of a thermally conductive material interspersed
with one or more catalyst materials for promoting the reforming
process, said plates being stacked together to form a reforming
structure, the plates conductively transferring heat energy
in-plane of the plates to support the reforming process.
34. The reformer of claims 32 or 33 wherein said reforming
structure includes at least one axial manifold for introducing the
reactant thereto and at least one manifold for allowing the
reaction species to exit from the reforming structure.
35. The reformer of claims 32 or 33 wherein said reforming
structure has an exposed peripheral surface for exchanging heat
energy with an external environment.
36. The reformer of claims 32 or 33 wherein said reforming
structure includes at least one axial reactant manifold for
introducing the reactant thereto and peripheral exhaust means for
exhausting the reaction species from a peripheral portion of the
reforming structure.
37. The reformer of claims 32 or 33 further comprising a thermally
conductive, gas-tight housing disposed about the reforming
structure to form a peripheral axial manifold, and means for
allowing the reaction species to enter the peripheral axial
manifold, wherein the reaction species is captured by the gas-tight
housing.
38. The reformer of claims 32 or 33 further including a thermally
conductive, gas-tight housing having means for exchanging heat
energy with the external environment and said reforming structure
by one of radiation, conduction and convection.
39. The reformer of claims 32 or 33 wherein an outer surface of the
reforming structure contacts an inner surface of a gas-tight
housing, said gas-tight housing being capable of conductively
transferring heat energy to the reforming structure.
40. The reformer of claims 32 or 33 further comprising a gas-tight
enclosure of cylindrical configuration for permitting pressurized
reformer operation.
41. The reformer of claims 32 or 33 wherein the reforming structure
includes means for providing a generally isothermal condition
through said reforming structure.
42. The reformer of claims 32 or 33 wherein said reforming
structure includes at least one axial reactant manifold for
introducing a reactant thereto, and wherein the reforming structure
includes extension means integrally formed therewith and extending
into the axial reactant manifold for preheating the reactant.
43. The reformer of claims 32 or 33 wherein said reforming
structure includes passage means for allowing a reactant to flow
through the structure.
44. The reformer of claims 32 or 33 further including an axial
manifold formed within the reforming structure, reactant passage
means for allowing a reactant to flow in-plane of the reforming
structure, and means for generating a reactant flow pressure drop
through the passage means that is substantially greater than the
reactant flow pressure drop within the axial manifold.
45. The reformer of claim 43 wherein the passage means maintains a
substantially uniform pressure drop to provide for a substantially
uniform flow of reactants along an axis of the reforming
structure.
46. The reformer of claims 32 or 33 further including means for
producing a substantially uniform temperature condition along an
axis of the reforming structure.
47. The reformer of claims 32 or 33 wherein the conductive material
is composed of at least one of a nonmetal such as silicon carbide,
and a composite material.
48. The reformer of claims 32 or 33 wherein the conductive material
is composed of at least one metal such as aluminum, copper, iron,
steel alloys, nickel, nickel alloys, chromium, chromium alloys,
platinum, and platinum alloys.
49. The reformer of claims 32 or 33 wherein the catalyst material
is selected from the group consisting of platinum, palladium,
nickel, nickel oxide, iron, iron oxide, chromium, chromium oxide,
cobalt, cobalt oxide, copper, copper oxide, zinc, zinc oxide,
molybdenum, molybdenum oxide, other transition metals and their
oxides.
50. The reformer of claims 32 or 33 wherein the reactant includes a
hydrocarbon species, and at least one of O.sub.2, H.sub.2O and
CO.sub.2.
51. The reformer of claims 32 or 33 further including means for
coupling the reaction species exiting the reformer to an external
fuel cell.
52. The reformer of claims 32 or 33 wherein the reactant includes a
hydrocarbon fuel and at least one of H.sub.2O and CO.sub.2 which
undergo catalytic reformation to produce H.sub.2, CO, H.sub.2O and
CO.sub.2, and wherein an exothermic reaction of an external fuel
cell supplements the energy requirements for the endothermic
reforming reaction of the reforming structure through the thermally
conductive material.
53. The reformer of claims 32 or 33 wherein the reactant includes a
hydrocarbon fuel and O.sub.2 which undergo catalytic combustion and
reformation to produce H.sub.2, CO, H.sub.2O and CO.sub.2, and at
least one of an exothermic combustion and an exothermic reaction of
an external fuel cell supplements the energy requirements for the
endothermic reforming reaction of the reforming structure through
the thermally conductive material.
54. The reformer of claims 32 or 33 wherein the reforming structure
has a substantially cylindrical shape.
55. The reformer of claims 32 or 33 wherein the reforming structure
is cylindrical and has a diameter between about 1 inch and about 20
inches.
56. The reformer of claims 32 or 33 wherein the reforming structure
has a substantially rectangular shape.
57. A burner for oxidizing a hydrocarbon fuel to produce heat
energy, said burner comprising: a plurality of conductive plates
formed of a thermally conductive material and a plurality of
catalyst plates having one or more oxidizing catalyst materials,
said catalyst plates and said conductive plates being alternately
stacked to form a burner structure; wherein the catalyst material
of the catalyst plate promotes the oxidation of the hydrocarbon
fuel to form a resultant species; and wherein the conductive plates
are capable of transferring heat energy produced during the
oxidation process to the surrounding medium by one of radiation,
conduction and convection.
58. The burner of claim 57 wherein the burner structure has an
exposed peripheral surface for exchanging heat energy with an
external environment.
59. The burner of claim 57 wherein said burner structure includes
at least one axial reactant manifold for introducing the reactant
thereto and peripheral exhaust means for exhausting the reaction
species from a peripheral portion of the burner structure.
60. The burner of claim 57 further including a thermally conductive
housing disposed about the burner structure and having means for
exchanging heat energy with the external environment and said
conductive plate by one of radiation, conduction and
convection.
61. The burner of claim 57 wherein an outer surface of the burner
structure contacts an inner surface of a thermally conductive
housing disposed about the burner structure, said housing
conductively transferring heat energy from the conductive plates
during operation.
62. The burner of claim 57 wherein the conductive plate includes
means for providing a generally isothermal condition, in plane of
the conductive plate.
63. The burner of claim 57 wherein said burner structure includes
at least one axial reactant manifold for introducing the reactant
thereto, and wherein the conductive plates include extension means
integrally formed thereon and extending into the axial reactant
manifold for preheating the hydrocarbon fuel.
64. The burner of claim 57 wherein an in-plane surface of at least
one of the conductive plate and the catalyst plate includes passage
means for allowing the hydrocarbon fuel to flow over the surface of
the plate.
65. The burner of claim 57 further including an axial manifold
formed within the burner structure, passage means formed in an
in-plane surface of one of the conductive plate and the catalyst
plate for allowing the fuel to flow over the surface of the plate,
and means for generating a reactant flow pressure drop through the
passage means that is substantially greater than the reactant flow
pressure drop within the axial manifold.
66. The burner of claim 64 wherein the passage means maintains a
substantially uniform pressure drop to provide for a substantially
uniform flow of reactants along an axis of the burner
structure.
67. The burner of claim 57 further including means for producing a
substantially uniform temperature condition along an outer surface
of the burner structure.
68. The burner of claim 64 wherein the catalyst plate is formed of
a porous catalyst material, the porous material forming the passage
means and allowing the reactant to pass through the plate.
69. The burner of claim 64 wherein the thermally conductive plate
is formed of a porous conductive material, the porous material
forming the passage means and allowing the reactant to pass through
the plate.
70. The burner of claim 57 wherein the conductive plate is composed
of silicon carbide.
71. The burner of claim 57 wherein the conductive plate is composed
of at least one refractory metal.
72. The burner of claim 57 wherein the catalyst plate is composed
of a ceramic support plate having the catalyst material coated
thereon.
73. The burner of claim 72 wherein the catalyst coating is selected
from the group consisting of at least one of platinum, nickel,
nickel oxide, chromium and chromium oxide.
74. The burner of claim 57 wherein the catalyst plate is composed
of at least one of platinum, nickel, nickel oxide, chromium and
chromium oxide.
75. The burner of claim 57 wherein the hydrocarbon fuel is
pre-mixed with an oxidizer reactant prior to introduction to or
within the axial manifold.
76. The burner of claim 57 wherein the burner structure has a
substantially cylindrical shape.
77. The burner of claim 57 wherein the burner structure is
cylindrical and at least one of the catalyst plate and the
conductive plate has a diameter between about 1 inch and about 20
inches, and has a thickness between about 0.002 inch and about 0.2
inch.
78. A burner for oxidizing a hydrocarbon fuel to produce heat
energy, said apparatus comprising: a porous and thermally
conductive material interspersed with one or more catalyst
materials to form a burner structure, wherein the catalyst material
promotes the oxidation of the hydrocarbon fuel to form a resultant
species, and wherein the conductive material is capable of
transferring heat energy produced during the oxidation process to
the surrounding medium by one of radiation, conduction and
convection.
79. A burner for oxidizing a hydrocarbon fuel to produce heat
energy, said apparatus comprising: a plurality of plates composed
of a thermally conductive material interspersed with one or more
catalyst materials, said plates being stacked together to form a
burner structure, wherein the catalyst material promotes the
oxidation of the hydrocarbon fuel to form a resultant species, and
wherein the conductive material transferring heat energy produced
during the oxidation process to the surrounding medium by one of
radiation, conduction and convection.
80. An electrochemical converter, comprising: a plurality of
gas-tight electrolyte plates having reactive materials disposed on
both sides thereof, said plates having a fuel flow side and having
the reactive material disposed thereon selected from the group
consisting of at least one of a combustion catalyst, a reforming
catalyst, a shift catalyst and a fuel electrode material, said
plates having an oxidant flow having the reactive material disposed
thereon selected from the group consisting of an oxidant electrode
material, a plurality of gas-tight conductive plates formed of a
thermally conductive material; said electrolyte plates and said
conductive plates being alternately stacked together to form a
stacked plate assembly, and internal reforming means for preheating
and reforming a hydrocarbon fuel on the fuel flow side of the
electrolyte plate within the stacked plate assembly, said reforming
being assisted by the conductive plates which are capable of
conductively transferring heat from a fuel cell reaction portion of
the stacked plate assembly.
81. The electrochemical converter of claim 80 wherein the
electrolyte plate forms a medium for the generation of an
electrolytic ionic transfer reaction.
82. The electrochemical converter of claim 80 wherein the converter
performs chemical transformation and production while consuming
oxygen to produce electricity.
83. The electrochemical converter of claim 80 wherein a side of the
conductive plate faces the fuel flow side having disposed thereon
at least one of the combustion catalyst, the reforming catalyst and
the shift catalyst.
84. The electrochemical converter of claim 80 wherein at least one
of the combustion catalyst, the reforming catalyst and the shift
catalyst can be applied on a flow adjustment element, said flow
adjustment element being situated between the electrolyte plate and
the conductive plate.
85. The electrochemical converter of claim 80 further comprising a
plurality of axial manifolds formed in the stacked plate assembly,
at least one of the manifolds being adapted to receive a
hydrocarbon fuel reactant and to allow the fuel to flow over one
surface of the electrolyte plate and to exit at the external edge
of the plates; and at least one other of said manifolds being
adapted to receive an oxidizer reactant and to allow the oxidizer
flow over the other side of the electrolyte plate and to exit at
the external edge of the plates.
86. The electrochemical converter of claim 80 wherein the stacked
plate assembly has a rectangular configuration with an edge that is
adapted to receive a hydrocarbon fuel reactant, said reactant
flowing into the space over one surface of the electrolyte plates
and exits from an opposing plate edge; and the third plate edge
being adapted to receive an oxidizer reactant that flows into a
space over the other surface of the electrolyte plate and exits
from a fourth plate edge.
87. The electrochemical converter of claim 80 wherein said
conducting plates include means for regulating the radial
temperature distribution of the stacked plate assembly to attain a
substantially in-plane isothermal condition.
88. The electrochemical converter of claim 85 wherein said
manifolds providing means for regulating the uniform flow
distribution into the spaces between the plates along the axis of
the stacked assembly to provide an axially isothermal
condition.
89. The electrochemical converter of claim 80 wherein the thermally
and electrically conductive material of the interconnector plate is
composed of at least a nonmetal.
90. The electrochemical converter of claim 80 wherein the thermally
and electrically conductive material of the interconnector plates
is composed of at least one of nickel, nickel alloys, chromium,
chromium alloys, platinum, and platinum alloys.
91. The electrochemical converter of claim 80 wherein the thermally
and electrically conductive material of the interconnector plate is
composed of at least one of aluminum, copper, iron, and steel
alloys.
92. The electrochemical converter of claim 80 wherein the fuel
electrode is composed of at least one of nickel, a nickel
containing compound, chromium and chromium containing compound.
93. The electrochemical converter of claim 80 wherein the
combustion catalyst is composed of at least one of platinum,
platinum compound, nickel and nickel compound.
94. The electrochemical converter of claim 80 wherein the reforming
catalyst is composed of at least one of nickel, a nickel containing
compound, chromium and a chromium containing compound.
95. The electrochemical converter of claim 80 wherein the reforming
catalyst is composed of at least one of platinum, palladium,
nickel, nickel oxide, iron, iron oxide, chromium, chromium oxide,
cobalt, cobalt oxide, copper, copper oxide, zinc, zinc oxide,
molybdenum, and molybdenum oxide.
96. The electrochemical converter of claim 80 wherein partial
oxidation at a location over the combustion catalyst formed on the
surface of the electrolyte plate.
97. The electrochemical converter of claim 80 wherein the internal
reforming reaction occurs over the reforming catalyst on the
surface of the electrolyte plate.
98. The electrochemical converter of claim 80 wherein the fuel cell
reaction occurs over the fuel electrode material on the surface of
the electrolyte plate.
99. The electrochemical converter of claim 80 wherein the reforming
catalyst and the fuel electrode material are intermixed over the
surface of the electrolyte plate to substantially simultaneously
reform the fuel and create electrochemical reaction during
operation.
100. The electrochemical converter of claim 80 wherein the
combustion catalyst, reforming catalyst and the fuel electrode
material are intermixed over the surface of the electrolyte plate
to substantially simultaneously initiate partial oxidation and
reformation of a fuel reactant.
101. The electrochemical converter of claim 80 wherein a
hydrocarbon fuel introduced to the converter catalytically reforms
in the presence of H.sub.2O, the fuel to produce H.sub.2 and CO,
said reformed fuel being subjected to a fuel cell reaction to form
an exhaust species containing H.sub.2O and CO.sub.2; wherein the
heat from the exothermic fuel cell reaction is conductively
transferred in-plane to the conductive plates to support the
endothermic reforming reaction.
102. The electrochemical converter of claim 80 wherein a
hydrocarbon fuel introduced to the converter catalytically combusts
partially with O.sub.2 to produce H.sub.2 and CO, said partially
combusted fuel being subjected to an exothermic fuel cell reaction
to form an exhaust species containing H.sub.2O and CO.sub.2,
wherein the heat generated from the exothermic fuel cell reaction
is conductively transferred in-plane to the conducting plates to
provide a temperature sufficient to support the mild exothermic
partial oxidation reforming reaction.
103. The electrochemical converter of claim 80 wherein the reactant
includes at least one of an alkane hydroxyl, a hydrocarbon bonded
with a carboxyl, a hydrocarbon bonded with a carbonyl, an olifin
hydrocarbon, a hydrocarbon bonded with an ether, a hydrocarbon
bonded with an ester, a hydrocarbon bonded with an amine, a
hydrocarbon bonded with an aromatic derivative, and a hydrocarbon
bonded other organo-derivatives.
104. The electrochemical converter of claim 80 wherein the
converter is a fuel cell selected from the group consisting of
solid oxide fuel cell, molten carbonate fuel cell, alkaline fuel
cell, proton exchange membrane fuel cell, and phosphoric acid fuel
cell.
105. The electrochemical converter of claim 80 wherein one side of
the electrolyte plate is composed of one of a zirconia based
materials and a ceria based material.
106. The electrochemical converter of claim 80 further including
internal reactant heating means disposed within one of the
manifolds for heating at least a portion of at least one of said
reactants passing through said manifold.
107. The electrochemical converter of claim 106 wherein said
internal reactant heating means comprises a thermally conductive
and integrally formed extended surface of said conductive plate
that protrudes into at least one of said manifolds.
108. The electrochemical converter of claim 107 wherein said fuel
cell reaction generates waste heat which heats said reactants to
about said operating temperature, said waste heat being
conductively transferred to said reactants by said interconnect
plate and said extended surface.
109. The electrochemical converter of claim 80 further including
peripheral exhaust means for exhausting the reformed fuel from a
peripheral portion of the stacked plate assembly.
110. The electrochemical converter of claim 80 wherein at least one
of the conductive plate and the electrolyte plate includes reactant
passage means for allowing the reactant to pass from the axial
reactant manifold over the surface of the plates.
111. The electrochemical converter of claim 110 wherein the passage
means includes means for maintaining a substantially uniform
pressure drop over at least one surface of the plates to provide
for a substantially uniform flow of reactant over the plate
surfaces.
112. The electrochemical converter of claim 110 wherein the
reactive coating of the electrolyte plate is porous, the porous
coating forming the reactant passage means.
113. The electrochemical converter of claim 80 further including
means for generating a reactant flow pressure drop through a space
formed between the conductive plate and the opposing electrolyte
plate that is substantially greater than the reactant flow pressure
drop within the axial manifold.
114. The electrochemical converter of claim 80 further including
means for producing a substantially uniform radial flow
distribution of reactants through said stacked plates.
115. The electrochemical converter of claim 80 wherein the stacked
plate assembly is cylindrical and at least one of the electrolyte
plate and the conductive plate has a diameter between about 1
inches and about 20 inches, and has a thickness between about 0.002
inches and about 0.2 inches.
116. The reformer of claim 80 further comprising a gas-tight
enclosure of cylindrical configuration configured to surround the
stacked plates to permit pressurized reformer operation.
117. The electrochemical converter of claim 80 wherein the
converter is an electrochemical catalytic converter which is
adapted to receive electricity from a remote power source, said
electricity initiating an electrochemical reaction within said
converter which is adapted to reduce selected pollutants contained
within the incoming reactants into benign species.
118. The electrochemical converter of claim 116 wherein the
catalytic converter further includes means to receive exhaust
containing selected pollutants, including NOx and hydrocarbon
species, the catalytic converter including means for reducing the
NOx and the hydrocarbon species into benign species, including one
of N.sub.2, O.sub.2 and CO.sub.2.
119. A catalytic converter, comprising a plurality of gas-tight
converter plates having disposed on a first hydrocarbon gas side a
reactive material consisting of one of a converter catalyst and a
first electrode material; and disposed on a second buffer gas side
a reactive material consisting of a second electrode material; a
plurality of gas-tight conductive plates formed of a thermally
conductive material; said converter plates and said conductive
plates being alternately stacked together to form a converter
assembly; means for introducing a hydrocarbon gas to the
hydrocarbon gas side of the converter plate and introducing a
buffer gas to the second buffer gas side of the converter plate;
means for receiving electricity from a remote power source; and
means for converting the hydrocarbon gas into benign species.
120. The converter of claim 108 wherein the conductive plates
includes means for attaining a generally isothermal condition
in-plane of the conductive plates.
121. The converter of claim 118 wherein the converter plate is
formed of a substantially gas tight electrolyte material.
122. The converter of claim 118 wherein the converter plate is a
gas tight ionic conductor.
123. The converter of claim 118 wherein the electrode coatings of
at least one side of the converter plate includes nickel or a
nickel containing compound.
124. The converter of claim 118 wherein the electrode coatings of
at least one side of the converter plate includes platinum.
125. The converter of claim 118 wherein the electrode coating of at
least one side of the converter plate includes palladium.
126. The converter of claim 118 wherein electricity received by
said converter initiates an electrochemical reaction which reduce
selected pollutants within the hydrocarbon gas into the benign
species. 127. The converter of claim 118 wherein the assembly is
adapted to receive exhaust containing selected pollutants,
including one of NOx and a hydrocarbon specie, the catalytic
converter further including means for reducing the NOx and
hydrocarbon species into benign species.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to reformers, and particularly
to reforming apparatus that reforms fuel into fuel species suitable
for use by electrochemical converters. In particular it relates to
a plate type reformer suitable for either steam reforming or
partial oxidation reforming.
[0002] The use of conventional hydrocarbon fuels as a fuel reactant
for fuel cells is well known in the art. The hydrocarbon fuels are
typically pre-processed and reformed into simpler reactants prior
to introduction to the electrochemical converter. Conventionally,
the fuel is pre-processed by passing the hydrocarbon fuel first
through a desulfurization unit, then through a reformer, and a
shift reactor (for H.sub.2 fueled fuel cell only) to produce a
suitable fuel stock.
[0003] Conventional steam reformers currently in wide commercial
use comprise a reformer section consisting of a catalyst material
which promotes the reforming reaction and a burner to supply heat
for the endothermic reforming reaction. A steam source is typically
connected to the reformer section to provide steam. The burner
typically operates at temperatures well above that required by the
reforming reaction and well above the operating temperatures of
conventional fuel cells, e.g., solid oxide fuel cells. Because of
this, the burner must be operated as a separate unit independent of
the fuel cell and as such adds considerable bulk, weight, cost and
complexity to the overall power system. Furthermore, the burner is
not uniquely adaptable to utilize the waste heat generally
available from the fuel cell. Moreover, the consumption of extra
fuel by the burner limits the efficiency of the power system.
[0004] A typical tubular reformer contains multiple tubes, which
are normally made of refractory metal alloys. Each tube contains a
packed granular or pelletized material having a suitable reforming
catalyst as a surface coating. The tube diameter typically varies
from between 9 cm and 16 cm, and the heated length of the tube is
normally between 6 and 12 meters. A combustion zone is provided
external to the tubes, and is typically formed in the burner. The
tube surface temperature is maintained by the burner in the range
of 900.degree. C. to ensure that the hydrocarbon fuel flowing
inside the tube is properly catalyzed with steam at a temperature
between 500.degree. C. and 700.degree. C. This traditional tube
reformer relies upon conduction and convection heat transfer within
the tube to distribute heat for reforming.
[0005] Plate-type reformers are known in the art, an example of
which is shown and described in U.S. Pat. No. 5,015,444 of Koga et
al. The reformer described therein has alternating flat gap spaces
for fuel/steam mixture flow and fuel/air mixture flow. The
combustion of the fuel/air stream within the spaces provides the
heat for reforming of the fuel/steam mixture stream. A drawback of
this design is that the reformer relies upon heat transfer between
the adjacent flat gap spaces to promote the fuel reforming
process.
[0006] U.S. Pat. No. 5,470,670 of Yasumoto et al. describes an
integrated fuel cell/reformer structure, which has alternating
layers of fuel cell and reformer plates. The heat transfer from the
exothermic fuel cell to the endothermic reformer occurs through the
thickness of the separating plates. A drawback of this design is
that it is difficult to attain, if at all, temperature uniformities
in this fuel cell/reformer structure, and which is essential in
compact and efficient chemical or electrochemical apparatus
designs. This fuel cell/reformer structure also requires complex
and cumbersome reactant manifolding to interconnect the reactant
flows between the alternating fuel cell layers and the reformer
layers.
[0007] Electrochemical converters, such as fuel cells, have been
known as systems for converting chemical energy derived from fuel
stocks directly into electrical energy through electrochemical
reaction. One type of fuel cell typically employed in fuel cell
power generation systems is a solid oxide fuel cell. The solid
oxide fuel cell generates electricity and releases waste heat at a
temperature of about 1000.degree. C.
[0008] A typical fuel cell consists mainly of a series of
electrolyte units, onto which fuel and oxidizer electrodes are
attached, and a similar series of interconnectors disposed between
the electrolyte units to provide serial electrical connections.
Electricity is generated between the electrodes across the
electrolyte by an electrochemical reaction that is triggered when a
fuel, e.g., hydrogen, is introduced at the fuel electrode and an
oxidant, e.g., oxygen, is introduced at the oxidizer electrode.
[0009] Typically, the electrolyte is an ionic conductor having low
ionic resistance thereby allowing the transport of an ionic species
from one electrode-electrolyte interface to the opposite
electrode-electrolyte interface under the operating conditions of
the converter. The electrical current can be tapped for external
load from the interconnector plates.
[0010] The conventional solid oxide fuel cell also includes, in
addition to the features listed above, an electrolyte having a
porous fuel and oxidizer electrode material applied on opposing
sides of the electrolyte. The electrolyte is typically an oxygen
ion conducting material, such as stabilized zirconia. The oxidizer
electrode, which is typically maintained in an oxidizing
atmosphere, is usually an perovskite of high electrical
conductivity, such as strontium doped lanthanum manganite
(LaMnO3(Sr). The fuel electrode is typically maintained in a fuel
rich or reducing atmosphere and is usually a cermet such as
zirconia-nickel (ZrO2/Ni). The interconnector plate of the solid
oxide fuel cell typically is made of an electronically conducting
material which is stable in both an oxidizing and reducing
atmosphere.
[0011] There still exists a need in the art for apparatus that
utilizes the waste heat generated by the fuel cell for reforming
use. In particular, there exists a need for employing reformer
design in close association with the electrochemical
converters.
[0012] The invention will next be described in connection with
certain preferred embodiments. However, it should be clear that
various changes and modifications can be made by those skilled in
the art without departing from the spirit and scope of the
invention.
SUMMARY OF THE INVENTION
[0013] It is an object of the present invention to provide a
plate-type reformer which has excellent thermal performance
characteristics and allows effective thermal integration with a
fuel cell. The invention further relates to a plate-type reformer
which may be operated either as a steam reformer or as a partial
oxidation reformer. When operating as a steam reformer it receives
heat from a source such as a fuel cell, and receives steam from a
source such as the exhaust of a fuel cell. The heat source can also
be a combustion reactor. When operating as a partial oxidation
reformer it combusts a relatively small portion, e.g., about 25%,
of the incoming reactant gas to provide heat for the endothermic
reforming reaction. The reformer is preferably capable of operating
at an autothermal balanced condition which requires no other
thermal input (heat source) nor steam supply. It is further capable
of operating at a partial oxidation condition which is able to
utilize the waste heat from a fuel cell.
[0014] Another object of the invention is to provide a plate-type
reformer in which the catalyst is in intimate thermal contact with
thermally conducting plates oriented, e.g., elongated, in the
direction of the gas flow so that an average in-plane plate
temperature is maintained to allow effective reforming reaction, as
well as to eliminate or reduce the occurrence of hot spots which
would be detrimental to the catalysts or structure materials of the
reformer. The term "in-plane" is intended to mean the flat surfaces
or side of the plate.
[0015] Still another object of the invention is to provide a
plate-type reformer which is capable of utilizing the waste heat
provided by the fuel cell for its endothermic reactions, either in
steam reforming or in partial oxidation reforming.
[0016] Yet, another object of the invention is to provide a
plate-type reformer which pre-heats the incoming reactants to a
temperature suitable for reforming.
[0017] Another object of the invention is to provide a plate-type
reformer in which multiple inlet manifolds are provided so that the
reactants may be introduced to the reformer separately, and which
are then thoroughly mixed within the reformer, before entering the
oxidation section and the reformer section of the reformer.
[0018] The reformer of the present invention employs a thermal
enhancement feature which promotes efficient fuel reformation.
According to one aspect, the reformer includes a planar catalyst
configuration having interleaved thermally conducting plates. The
latter feature greatly enhances the thermal characteristics of the
reformer, resulting in a relatively compact reformer design. Hence,
the reformer can be thermally and physically integrated with an
electrochemical converter for efficiently reforming hydrocarbon
fuel and generating electricity.
[0019] The invention overcomes the size disadvantages of
conventional reformers by utilizing the foregoing efficient heat
transfer techniques to achieve temperature uniformity (isothermal
surfaces) and energy balance in the system. This temperature
uniformity reduces the amount of reforming material necessary to
reform the incoming reactants. Furthermore, the thermal energy
required by the endothermic reforming reactions is derived from the
waste heat of the thermally integrated electrochemical converter.
For example, under normal operating conditions the converter
generates excess or waste heat, which is used to support an
operating temperature consistent with that required for reforming
(in the range between about 500.degree. C. and about 700.degree.
C.).
[0020] Other general and more specific objects of the invention
will in part be obvious and will in part be evident from the
drawings and description which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The foregoing and other objects, features and advantages of
the invention will be apparent from the following description and
apparent from the accompanying drawings, in which like reference
characters refer to the same parts throughout the different views.
The drawings illustrate principles of the invention and, although
not to scale, show relative dimensions.
[0022] FIG. 1 is a cross-sectional view of one embodiment of an
external fuel reformer according to the present invention;
[0023] FIGS. 2A-2C are cross-sectional views of various embodiments
of the catalyst and reforming plates of FIG. 1.
[0024] FIG. 3 is an isometric view of an assembled electrochemical
converter with internal reforming capability;
[0025] FIG. 4 is a more detailed isometric view of the electrolyte
component and the interconnector component of an electrochemical
converter allowing internal reforming;
[0026] FIG. 5 is a cross-sectional assembled view of the
electrolyte component and interconnector component according to the
invention. illustrating the flow of reactants therethrough of
external manifolding; and
[0027] FIG. 6 graphically illustrates that the interconnector
plates provide the heat transfer function among the endothermic
reforming strip and the exothermic combustion strip and the
exothermic fuel cell strip, resulting in an isothermal in-plane
temperature.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0028] FIG. 1 is a cross-sectional view of the reformer 10 of the
present invention. The reformer 10 includes a number of thermally
conductive plates 12 and reforming plates 14 that are alternately
stacked together to form a stacked reforming structure 13 that
extends along axis 28. The reformer includes a fluid conduit 16
that is in fluid communication with the inner portions 12A, 14A of
the plates 12, 14. The reformer 10 is preferably housed within a
gas-tight enclosure or housing 20. The illustrated reformer can be
used to perform both steam and oxidation reforming. The heat
necessary for the reforming process can be supplied internally by
partial oxidation of hydrocarbon fuel or supplied externally by a
remote heat source, as shown by wavy lines 26, to the reformer 10
by radiation, conduction or convection.
[0029] The reactant to be reformed by the reformer 10 is introduced
into the apparatus through the axial fluid manifold 16. The
reactant preferably comprises a mixture of a hydrocarbon fuel and a
reforming agent, such as air, oxygen, water or CO.sub.2, that are
premixed either prior to introduction to the manifold 16 or within
the reformer. The illustrated reformer 10 includes at least one
manifold that delivers a fuel/reforming agent mixture to the
reformer, rather than provide separate input manifolds for each gas
constituent. The introduction of a premixed reactants to the
reformer 10 provides for a relatively simple design.
[0030] The reactant mixture 22 is introduced to the manifold 16 by
any appropriate means, such as by fluid conduits. The mixture 22
enters the inner portions of the reformer through reactant passages
24 that are formed between the adjacent conductive plates 12 and
reforming plates 14. The passages can comprise any surface
indentation or protrusions, which can be formed by embossing, and
which constitutes a substantially continuous fluid passage that
extends from the manifold 16 to the outer peripheral surface 13A of
the stacked reforming structure 13. The passages can also be formed
by utilizing conductive or reforming plates that are made of a
porous material or have a power reformer catalyst material coated
or formed thereon, thus allowing the reactant to pass through the
reformer.
[0031] Examples of these various plate arrangements and
configurations are illustrated in FIGS. 2A-2C. FIG. 2A illustrates
the stacked arrangement of the reformer plates 14 and conductive
plates 12. The reformer plates preferably have formed thereon a
reformer catalyst material 36 that intimately contacts the
conductive plate 12. The illustrated conductive plate 12 is
embossed to form reactant flow channels. The mixture 22 is
introduced to the axial manifold 16 and enters the reactant
channels, where it exits the stacked plate reformer at the
peripheral edges thereof.
[0032] The reformer catalyst material can be composed of a solid or
porous material. FIG. 2B illustrates the mixture flow through the
reformer 10 when using a porous reforming material. The use of a
porous reforming material relaxes the embossing requirements of the
illustrated reformer.
[0033] In another embodiment, as illustrated in FIG. 2C, the
reformer 10 includes a plurality of stacked plates 38 or simply a
columnal structure that are formed of a composite of thermally
conductive material and a reforming material. This composite plate
38 can be achieved by interspersing a suitably thermally conductive
material in admixture with a suitable reforming material. The
resultant stacked structure operates substantially identical to the
stacked reforming structure 13 shown in FIGS. 1, 2A and 2B and
described above.
[0034] Those of ordinary skill will recognize that other
embodiments of the reformer 10 exists, such as where the reforming
plates 14 are composed of a porous material and have a reforming
catalyst material disposed therein or coated thereon. The use of
porous materials is one of the advantages of the present external
reformer since it relaxes the gas-tight requirements of the
reforming system without sacrificing efficiency.
[0035] The reactant mixture is reformed within the stacked
reforming structure 10 as the reactant passes through the reactant
passages and over or through the reforming plates 14. The catalyst
material associated with the reforming plates 14 promotes the
reforming of the hydrocarbon fuel into simpler reaction species.
The stream of reactant mixture introduced to the manifold 16 can
comprise H.sub.2O, O.sub.2, and CO.sub.2, in addition to a
hydrocarbon fuel. For example, methane (CH.sub.4) can be
catalytically reformed into a mixture of hydrogen, water, carbon
monoxide and carbon dioxide.
[0036] When operating the reformer as a steam reformer, it receives
a reactant gas mixture containing natural gas (or methane) and
steam. Steam reforming catalyst can be formed on the reformer plate
in a circumferential band. Thermal energy for the reforming
reaction is preferably conducted radially inward from the gas-tight
enclosure by the conductive plates 12. The thickness and thermal
conductivity of the conductive plates are selected to provide
sufficient heat flow radially (or in-plane) to provide heat for the
endothermic reforming reaction. The conductive plate can include an
integral extension which protrudes into the axial reactant manifold
16 for preheating the incoming reactants, as described in further
detail below.
[0037] When operating the reformer as a partial oxidation reformer,
it receives a reactant gas mixture containing natural gas (or
methane) and air or oxygen. One or more types of reforming catalyst
material can be distributed in circumferential bands on the
reformer plate. According to one aspect, the plate can include an
inner band which contains a combustion catalyst 92, and a radially
outer band 90 which contains catalyst to promote reforming of
methane by water vapor (steam reforming) and by carbon dioxide.
Thermal energy for these endothermic reforming reactions is
conducted radially from the combustion band to the reforming band
by the plate 12. Catalysts for other reactions, such as
conventional shift reactions that convert CO in the presence of
H.sub.2O to form H.sub.2 and CO.sub.2 may also be incorporated. The
thickness and thermal conductivity of the conductive plates 12 are
selected to provide sufficient heat flow radially between the inner
combustion band and the outer reforming band to supply heat energy
for the endothermic reforming reactions. The conductive plates 12
also provide sufficient heat flow radially from the combustion band
to pre-heat the incoming reactants at the inlet passages 24 to near
operational temperatures, e.g., at least about 300.degree. C. The
thermal energy of the system is preferably transferred from the
external source to the reformer 10 through the gas-tight enclosure
20.
[0038] The illustrated reformer 10 can be used to reform reactants
such as alkanes (paraffin hydrocarbons), hydrocarbons bonded with
alcohols (hydroxyls), hydrocarbons bonded with carboxyls,
hydrocarbons bonded with carbonyls, hydrocarbons bonded with
alkenes (olifins hydrocarbons), hydrocarbons bonded with ethers,
hydrocarbons bonded with esterhydrocarbons bonded with amines,
hydrocarbons bonded with aromatic derivatives, and hydrocarbons
bonded other organo-derivatives.
[0039] The band of reforming material of the reformer 10 can be
located and mixed in varying proportions to maximize the production
of reformed gas.
[0040] The reforming plate 14 can be composed of any suitable
reforming catalytic material that operates at temperatures in the
range between about 200.degree. C. and about 800.degree. C.
Examples of the types of material that can be used include
platinum, palladium, chromium, chromium oxide, nickel, nickel
oxide, nickel containing compounds, and other suitable transition
metals and their oxides. The reforming plate 14 can further include
a ceramic support plate that has a reforming material coated
thereon, as illustrated in FIGS. 2A and 2B. Thus, the reforming
plate 14 of the present invention can include any multi-stacked
reforming plate structure that includes suitable reforming
catalysts that promote the reformation of a hydrocarbon fuel into
suitable reaction species.
[0041] The conductive plate 12 can be formed of any suitable
thermally conductive material, including metals such as aluminum,
copper, iron, steel alloys, nickel, nickel alloys, chromium,
chromium alloys, platinum, and nonmetals such as silicon carbide,
and other composite materials. The thickness of the conductive
plate 12 can be selected to maintain a minimum temperature gradient
in-plane of the plate 12 and to thereby provide an isothermal
region for optimum reforming reaction and to alleviate thermal
stress in the reforming plates 14. The conductive plate 12
preferably forms a near isothermal condition in-plane of each plate
12. The isothermal surface formed by the conductive plate 12
improves the efficiency of the overall reforming process by
providing a substantially uniform temperature and supply of heat
over the surface of the plate for reforming.
[0042] Furthermore, the conductive plates form an isothermal
condition along the axis of the stack (along the outer peripheral
surface of the stacked reformer 13) by the uniform distribution of
the reactant mixture through the reactant passages, thereby
preventing cold or hot spots from developing along the stack. This
improves the thermal characteristics of the reformer 10 and
improves the overall performance of the system. As used herein, the
term "isothermal" condition or region is intended to include a
substantially constant temperature that varies only slightly in an
axial or in-plane direction. A temperature variation of at least
about 50.degree. C. is contemplated by the teachings of the present
invention.
[0043] The reformed fuel or reaction species is exhausted along the
peripheral portion 13A of the stacked reforming structure 13, as
indicated by wavy lines 30. The peripheral exhausting of the
reaction species, e.g., reformed fuel products allows relatively
easy manifolding of the reactants. The exhausted fluid media are
then collected by the gas-tight housing 20 and exhausted therefrom
through exit conduits 32. The gas-tight housing 20 thus serves as a
peripheral manifold.
[0044] In an alternate embodiment, the reactant mixture 22 can be
introduced into the peripheral manifold formed by the housing 20
and then into the stacked reforming structure 13 along the
peripheral edge. The reactant flows radially inward across the
reforming and conductive plates 14, 12 and is discharged through
the axial manifold 16.
[0045] The ability to vent the reformed reactant mixture at least
at a substantial portion of the periphery of the stack, and
preferably from nearly the entire periphery, provides for an
exposed peripheral surface devoid of a gas-tight seal or insulating
material. Hence, the external reformer 10 of the present invention
achieves a compact, simple, elegant external reforming design.
[0046] The gas-tight enclosure 20 is preferably composed of a
thermally conductive material, such as metal. In the illustrated
embodiment, the gas-tight enclosure 20 radiantly receives heat
energy from an external heat source and further radiantly transfers
this heat energy to the stack 13 and thus to the conductive plates
12. The plates 12 supply the heat energy necessary for the
reforming reaction by conductively transferring the heat from the
outer peripheral surface 13A of the stack 13 inwardly towards the
reactant manifold 16.
[0047] In another embodiment, the outer surface of the reforming
structure 10 contacts the inner surface of the gas-tight housing,
which serves to conductively transfer the heat energy to the
conductive plates.
[0048] The gas-tight enclosure of cylindrical configuration is
particularly suitable for pressurized reformer operation. The
pressure within the vessel is preferably between about ambient and
about 50 atm.
[0049] The technique for achieving axial reactant flow distribution
uniformity is as follows. The reactant flow passages 24 are
designed to ensure that the total reactant flow pressure drop in
the reactant passages is significantly greater than or dominates
the reactant flow pressure drop in the reactant manifold 16. More
specifically, the flow resistance of the passages 24 is
substantially greater than the flow resistance of the axial
manifold 16. According to a preferred practice, the reactant flow
pressure within the passages 24 is about ten times greater than the
reactant flow pressure within the manifold. This pressure
differential ensures an axial and azimuthal uniform distribution of
reactant along the reactant manifold 16 and the reactant passages
24 and essentially from top to bottom of the reformer stack 13. The
uniform flow distribution ensures a uniform temperature condition
along the axis of the reforming structure 10.
[0050] According to a preferred embodiment, the stacked reforming
structure 13 is a columnal structure, and the plates have a
diameter between about 1 inch and about 20 inches, and has a
thickness between about 0.002 inch and about 0.2 inch. The term
columnal as used herein is intended to describe various geometric
structures that we stacked along a longitudinal axis and have at
least one internal reactant manifold which serves as a conduit for
a reactant mixture.
[0051] Those of ordinary skill will appreciate that other geometric
configurations can be used, such as rectangular or rectilinear
shapes with internal or external manifolds. The plates having a
rectangular configuration can be stacked and integrated with
attached external manifolds for the supply and the collection of
the reactant and reforming resultant species.
[0052] The relatively small dimensions of the plates 12, 14 of the
reformer 10 provide for a compact plate-type reformer that reforms
a hydrocarbon fuel into suitable reaction species, and which is
easily integratable with existing power systems and assemblies. The
illustrated reformer 10 can be thermally integrated with an
electrochemical converter, such as a solid oxide fuel cell. In the
special application where the reformed fuel is introduced into the
fuel cell, the required heat of reaction is supplied from the waste
heat generated by the fuel cell.
[0053] According to another practice of the present invention, the
reformer structure of FIG. 1 can also function as-a plate-type
burner. Specifically, hydrocarbon fuel can be oxidized in the
presence of air or other oxidants with or without a suitable
catalyst material. The burner embodiment of the present invention
includes a conductive plate 12 and a catalyst plate 14 that are
alternately stacked together, as described above in relation to the
reformer of FIG. 1. The burner can employ an input manifold 16 to
introduce the incoming reactant to the burner. The incoming
reactants can comprise a hydrocarbon fuel and an oxidant, such as
air. The hydrocarbon fuel and oxidant can be separately manifolded
to the burner or can be premixed. For example, if substantially
gas-tight materials are used to form the plates 12, 14, the
reactants are premixed either prior to introduction to the burner
or within the input manifold. Conversely, if either plate is formed
of a porous material, the reactants can be separately manifolded.
The reactants passing across the porous material of the plate then
pass therethrough and mix with the other reactant within the
reactant passages. The combusted or oxidized reactant is then
discharged about the periphery of the burner stack. The oxidized
reactant or the resultant species includes CO.sub.2, H.sub.2O and
other stable combustion products depending upon the type of
fuel.
[0054] The conductive plate of the burner is identical to that of
the reformer and functions to conductively transfer heat in-plane
of the plate to form an isothermal surface. The thickness of the
conductive plate is designed to maintain a minimum temperature
gradient in-plane of the plate to provide an isothermal region for
optimum combustion reaction to produce reduced NOx, if air is used
as the oxidant, and to alleviate thermal stress in the catalyst
plates 14.
[0055] Furthermore, the isothermal condition can be maintained by
the uniform distribution of reactants of along the axis of the
stack, thus preventing cold hot spots from developing along the
stack. This improves the overall thermal characteristics of the
burner and improves the overall operating performance of the
burner.
[0056] The illustrated burner further includes reactant flow
passages 24, as set forth above in conjunction with the reformer
10. The reactant passages 24 are designed to ensure that the total
reactant flow pressure drop in the reactant passages 24 is
significantly greater than the reactant flow pressure drop in the
reactant manifold 16. More specifically, the flow resistance the
passages 24 is substantially greater than the flow resistance in
the axial manifold 16. This pressure differential ensures an axial
and azimuthal uniform distribution of reactant throughout the axial
length of the burner.
[0057] The oxidized reactant can be discharged about the peripheral
portion of the burner. The exhausted fluid mediums can be captured
by a gas-tight housing 20 that surrounds the burner.
[0058] In an alternate embodiment, the burner can include a
plurality of stacked plates that are formed of a composite of a
thermally conductive material and a catalyst material. This
composite plate can be achieved by interspersing a suitably
thermally conductive material in admixture with a suitable
catalytic material. The resulting stacked structure operates
substantially identical to the stacked reforming structure 13 shown
in FIG. 1 and described above.
[0059] In an alternate embodiment, the burner can include a
cylindrical column that is formed of a composite of a thermally
conductive material and a catalyst material by interspersing a
suitably thermally conductive material in admixture with a suitable
catalytic material. The resulting reforming structure operates
substantially identical to the stacked reforming structure 13 shown
in FIG. 1 and described above.
[0060] All other features discussed above in relation to the
reformer are equally applicable to the burner.
[0061] FIG. 3 shows an isometric view of a reformer incorporated
internal to an electrochemical converter according to a preferred
embodiment of the invention. The internal reforming electrochemical
converter 40 is shown consisting of alternating layers of an
electrolyte plate 50 and an interconnector plate 60. The
interconnector plate is typically a good thermal and electrical
conductor. Holes or manifolds formed in the structure provide
conduits for the fuel and oxidizer gases, e.g., input reactants.
Reactant flow passageways formed in the interconnector plates, FIG.
4, facilitate the distribution and collection of these gases.
[0062] The plates 50, 60 of the internal reforming electrochemical
converter 40 are held in compression by a spring loaded tie-rod
assembly 42. The tie-rod assembly 42 includes a tie-rod member 44
seated within a central oxidizer manifold 47, as shown in FIG. 4,
that includes an assembly nut 44A. A pair of endplates 46 mounted
at either end of the internal reforming electrochemical converter
40 provides uniform clamping action on stack of alternating
interconnector and electrolyte plates 50, 60 and maintains the
electrical contact between the plates and provides gas sealing at
appropriate places within the assembly.
[0063] FIGS. 3 through 5 illustrate the basic cell unit of the
electrochemical converter 40, which includes the electrolyte plate
50 and the interconnector plate 60. In one embodiment, the
electrolyte plate 50 can be made of a ceramic material, such as a
stabilized zirconia material ZrO.sub.2(Y.sub.2O.sub.3), an oxygen
ion conductor, and a porous oxidizer electrode material 50A and a
porous fuel electrode material 50B which are disposed thereon.
Exemplary materials for the oxidizer electrode material are
perovskite materials, such as LaMnO.sub.3(Sr). Exemplary materials
for the fuel electrode material are cermets such as ZrO.sub.2/Ni
and ZrO.sub.2/NiO.
[0064] The interconnector plate 60 preferably is made of an
electrically and thermally conductive interconnect material. The
materials suitable for interconnector fabrication include metals
such as aluminum, copper, iron, steel alloys, nickel, nickel
alloys, chromium, chromium alloys, platinum, platinum alloys, and
nonmetals such as silicon carbide, La(Mn)CrO.sub.3, and other
electrically conductive materials. The interconnector plate 60
serves as the electric connector between adjacent electrolyte
plates and as a partition between the fuel and oxidizer reactants.
Additionally, the interconnector plate 60 conductively transfers
heat in-plane (e.g., across the surface) of the plate to form an
isothermal surface, as described in further detail below. As best
shown in FIG. 4, the interconnector plate 60 has a central aperture
62 and a set of intermediate, concentric radially outwardly spaced
apertures 64. A third outer set of apertures 66 are disposed along
the outer cylindrical portion or periphery of the plate 60.
[0065] The interconnector plate 60 can have a textured surface. The
textured surface 60A preferably has formed thereon a series of
dimples, which are formed by known embossing techniques and which
form a series of connecting reactant flow passageways. Preferably,
both sides of the interconnector plate have the dimpled surface
formed thereon. Although the intermediate and outer set of
apertures 64 and 66, respectively, are shown with a selected number
of apertures, those of ordinary skill will recognize that any
number of apertures or distribution patterns can be employed,
depending upon the system and reactant flow and manifolding
requirements.
[0066] Likewise, the electrolyte plate 50 has a central aperture
52, and a set of intermediate and outer apertures 54 and 56 that
are formed at locations complementary to the apertures 62, 64 and
66, respectively, of the interconnector plate 60.
[0067] As shown in FIG. 4, a reactant flow adjustment element 80
can be interposed between the electrolyte plate 50 and the
interconnector plate 60. The flow adjustment element 80 serves as a
fluid-flow impedance between the plates 50, 60, which restricts the
flow of the reactants in the reactant flow passageways. Thus, the
flow adjustment element 80 provides for greater uniformity of flow.
A preferred flow adjustment element is a wire mesh or screen, but
any suitable design can be used provided it serves to restrict the
flow of the reactants at a selected and determinable rate.
[0068] Referring to FIG. 4, the electrolyte plates 50 and the
interconnector plates 60 are alternately stacked and aligned along
their respective apertures. The apertures form axial (with respect
to the stack) manifolds that feed the cell unit with the input
reactants, and that exhaust spent fuel. In particular, the central
apertures 52, 62 form input oxidizer manifold 47, the concentric
apertures 54, 64 form input fuel manifold 48, and the aligned outer
apertures 56, 66 form spent fuel manifold 49.
[0069] The absence of a ridge or other raised structure at portion
of the periphery of the interconnector plate provides for exhaust
ports that communicate with the external environment. The reactant
flow passageways connect, fluidwise, the input reactant manifolds
47 and 48 with the outer periphery of the reformer 40, thus
allowing the reactants to be exhausted externally of the
converter.
[0070] The internal reforming electrochemical converter is a
stacked plate assembly of cylindrical configuration, and at least
one of the electrolyte plate and the conductive plate has a
diameter between about 1 inches and about 20 inches, and has a
thickness between about 0.002 inches and about 0.2 inches.
[0071] The internal reforming electrochemical converter 40 of this
invention has incorporated therein additional features as described
below. The internal reforming operation when performed in the
presence of steam receives a reactant gas mixture containing
natural gas (or methane) and steam. A steam reforming catalyst 90,
(FIG. 5) is distributed in a circumferential band that precedes the
fuel electrode material 50B on the electrolyte plate 50. Thermal
energy for the reforming reaction is conducted radially by the
plate 60 to the reforming band. The thickness and thermal
conductivity of the plates is designed to provide sufficient heat
flow radially between the inner reforming band 90 and the outer
fuel cell band (e.g., band 50B) to provide heat energy for the
endothermic reforming reaction and to pre-heat the incoming
reactants.
[0072] The internal reforming can also be performed by a partial
oxidation reaction. In this mode, the illustrated converter 40
receives a reactant gas mixture containing natural gas (or methane)
and air or oxygen. One or more types of catalyst are distributed in
circumferential bands preceding the fuel electrode 50B on the
electrolyte plate 50. As shown in FIG. 5, the electrolyte plate
includes an inner band that contains a combustion catalyst 92, a
radially outer band 90 that contains catalysts to promote reforming
of methane by water vapor (steam reforming) and by carbon dioxide.
Thermal energy for these endothermic reforming reactions is
conducted radially from the combustion band 92 to the reforming
band 90. Catalysts for other reactions, e.g. shift reactions etc.
may also be incorporated. The thickness and thermal conductivity of
the conductive plates is designed to provide sufficient heat flow
radially between the inner combustion band 90 and the radially
outer reforming band 90 to provide the endothermic reaction energy
and to pre-heat the incoming reactants. Additional thermal energy
can be obtained from the exothermal fuel cell reaction performed by
the fuel electrode 50B illustrated as an outermost band along the
diameter of the plate.
[0073] In the illustrated electrochemical converter 40, the
combustion catalyst 92, the reforming catalyst 90 and a shift
catalyst (which can be also applied as a band radially outward of
the reforming catalyst 80) can also be applied on the flow
adjustment element, which is situated between the electrolyte plate
and the conductive plate.
[0074] The reformer may apply the catalysts which are mixed in
varying proportions radially to maximize the production of product
gas.
[0075] All of the reforming features discussed above in relation to
the external reformer and band are equally applicable to this
internal reforming electrochemical converter. For example, the
interconnector plate 60 can include extended lip portions 72A and
72B, either of which can be used to preheat incoming reactants.
[0076] The internal reforming electrochemical converter 40 of the
present invention can be a fuel cell, such as a solid oxide fuel
cell, molten carbonate fuel cell, alkaline fuel cell, phosphoric
acid fuel cell, and proton membrane fuel cell. The preferred fuel
cell of the present invention is a solid oxide fuel cell. The
internal reforming electrochemical converter 40 of the present
invention preferable has an operating temperature above 600.degree.
C., and preferably between about 900.degree. C. and 1100.degree.
C., and most preferably about 1000.degree. C.
[0077] Those of ordinary skill will appreciate that the illustrated
combustion, reforming and fuel electrode bands are merely
representative of relative locations of electrochemical operations
that occur during use of the converter 40 as a reformer.
[0078] In another embodiment of the invention, the internal
reforming electrochemical converter 40 can have any desirable
geometric configuration, such as a rectilinear configuration. The
stacked structure can thus include rectangular electrolyte plates
50 and rectangular interconnector plates 60 with manifolds attached
external to the plates. The catalytic and electrode materials can
be applied in strips on the electrolyte plates perpendicular to the
reactants flow direction. As illustrated in FIG. 5, the fuel flow
24 is perpendicular to the elongated bands 92, 90 and 50B. The
interconnector plates 60 conductively transfer heat energy to the
endothermic reforming catalyst band 90, the exothermic combustion
catalyst band 92, and the exothermic fuel cell band 50B, resulting
in a substantially in-plane isothermal condition, as illustrated in
FIG. 6.
[0079] FIG. 6 graphically depicts the isothermal temperature
condition of the incoming reactants, e.g., hydrocarbon fuel, and
reformed fuel established by the thermally conductive plate 60
during its passages over the electrolyte plate 50. The temperature
of the fuel during operation is defined by the ordinate axis and
the fuel flow direction is defined by the abscissa. In a reforming
structure that does not utilize a thermally conductive plate to
transfer heat in-plane during operation, the fuel temperature
varies greatly in the direction of fuel flow, as denoted by
waveform 110. As illustrated, the incoming fuel is initially
preheated, as by the extended surfaces 72A and 72B. This preheating
stage 112 corresponds to a rise in the fuel temperature as it
approaches the operating temperature of the converter 40. During
the exothermic partial oxidation or combustion stage 114, the
temperature of the fuel further increases until the fuel flow
reaches the reformation stage 116. The endothermic reformation
stage requires a significant amount of heat energy to sustain the
reforming operation. The fuel than flows to the fuel cell reaction
stage 118, where the fuel is again heated, e.g., by the relatively
hot operating environment of the converter 40. This sinusoidal like
temperature profile 110 of the fuel decreases the overall operating
efficiency of the converter, as well as exposes certain components
(the electrolyte plate 50) to undesirable thermal stresses. The
introduction of the conductive (interconnector) plate within the
converter 40 "smoothes" the temperature profile and creates a
substantially isothermal temperature condition, in-plane and
axially along the converter stack, through all stages of operation
as illustrated by the isothermal profile 120.
[0080] According to one mode of operation, the internal reforming
electrochemical converter catalytically reforms the hydrocarbon
fuel with H.sub.2O to produce H.sub.2 and CO, which in turn
proceeds to the fuel cell portion (e.g., fuel electrode 50B) for
electricity generation. It produces exhaust species H.sub.2O and
CO.sub.2. The heat from the exothermic fuel cell reaction is
conductively transferred in-plane to the conducting plates to
support the endothermic reforming reaction.
[0081] According to another mode of operation, the internal
reforming electrochemical converter catalytically oxidizes
hydrocarbon fuel to produce H.sub.2 and CO, which proceeds to the
fuel cell section for electricity generation. It produces exhaust
species H.sub.2O and CO.sub.2. The heat from the exothermic fuel
cell reaction is conductively transferred in-plane to the
conductive plates 60 to support the mildly exothermic partial
oxidation reforming reaction.
[0082] The internal reforming electrochemical converter can be
placed in an enclosure designed for pressurized operation.
[0083] Another significant feature of the present invention is that
the extended heating surfaces 72D and 72C heat the reactants
delivered from the oxidizer and fuel external manifolds 47 and 48
to the operating temperature of the converter. Specifically, the
extended surface 72D that protrudes into the oxidizer manifold 47
heats the oxidizer reactant, and the extended surface 72C that
protrudes into the fuel manifold 48 heats the fuel reactant. The
highly thermally conductive interconnector plate 60 facilitates
heating of the input reactants by conductively transferring heat
from the fuel cell strip to the extended surfaces or lip portions,
thus heating the input reactants to the operating temperature. The
extended surfaces thus function as a heat fin. This reactant
heating structure provides a compact converter that is capable of
being thermally integrated into a power system to realize
extraordinary system efficiency.
[0084] The illustrated electrochemical converter 40 of FIGS. 3-5 is
also capable of performing chemical transformation and production,
while concomitantly producing electricity in a coproduction
operation.
[0085] According to this embodiment, the electrochemical converter
40 is adapted to receive electricity from a power source, which
initiates an electrochemical reaction within the converter and
reduces selected pollutants contained within the incoming reactant
into benign species. Hence, for example, the electrochemical
converter 40 can be coupled to an exhaust source that contains
selected pollutants, including NOx and hydrocarbon species. The
converter 40 catalytically reduces the pollutants into benign
species, including N.sub.2, O.sub.2 and CO.sub.2.
[0086] It will thus be seen that the invention efficiently attains
the objects set forth above, among those made apparent from the
preceding description. Since certain changes may be made in the
above constructions without departing from the scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings be interpreted as
illustrative and not in a limiting sense.
[0087] It is also to be understood that the following claims are to
cover all generic and specific features of the invention described
herein, and all statements of the scope of the invention which, as
a matter of language, might be said to fall therebetween.
* * * * *