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A solid oxide fuel cell system including a main plate, an inner cylinder attached to the main plate, an intermediate cylinder attached to the main plate such that the intermediate cylinder contains a cathode air stream, and an outer cylinder attached to the main plate. An exhaust annular gap is form

A solid oxide fuel cell system including a main plate, an inner cylinder attached to the main plate, an intermediate cylinder attached to the main plate such that the intermediate cylinder contains a cathode air stream, and an outer cylinder attached to the main plate. An exhaust annular gap is formed between the intermediate and outer cylinders such that hot exhaust gases flow through the exhaust annular gap and heat is transferred from the hot exhaust gases to the cathode air stream. The solid oxide fuel cell system may also include a two-stage tail gas combustor.

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1. A solid oxide fuel cell system comprising: a stack including a bundle of tubular cells;a feed tube extending through the stack for providing an anode feed stream;an inlet end tube sheet for retaining a position of the tubular cells;a partial cylinder end cap sealed to the inlet end tube sheet to

1. A solid oxide fuel cell system comprising: a stack including a bundle of tubular cells;a feed tube extending through the stack for providing an anode feed stream;an inlet end tube sheet for retaining a position of the tubular cells;a partial cylinder end cap sealed to the inlet end tube sheet to form an anode feed plenum having a reducing environment, wherein the anode feed plenum is in fluid communication with the feed tube so that the anode feed stream passes through the stack to become an anode exhaust;a main plate supporting the stack and forming an exhaust plenum into which the anode exhaust flows, the main plate defining at least one feed hole;an inner cylinder attached to the main plate and enclosing the stack and end cap to form a cathode feed plenum so that a cathode gas stream mixes with the anode exhaust in the exhaust plenum to form an exhaust flow; anda hot zone boundary element coupled to the main plate and having: i) a cap defining a flame space with the main plate; ii) a tail gas combustor at least partially located in the flame space, wherein the exhaust flow enters the tail gas combustor by the at least one feed hole and becomes a heated exhaust stream; and iii) an outer cylinder coupled to the cap and enclosing the inner cylinder to define an exhaust annular gap around the inner cylinder, wherein the heated exhaust stream exits through the exhaust annular gap and, in turn, exchanges heat with the cathode feed plenum. 2. A solid oxide fuel cell system as recited in claim 1, wherein the feed tube extends centrally through the stack and has a CPOX reactor therein so that flow from the CPOX reactor is directed into the anode feed plenum. 3. A solid oxide fuel cell system as recited in claim 1, wherein the tail gas combustor includes a first non-noble metal catalyst stage in the flame space and a second catalytic stage in the exhaust annular gap. 4. A solid oxide fuel cell system comprising: a main plate;a stack supported by and depending from the main plate, the stack having anodes and cathodes, wherein the main plate defines an exhaust plenum with the stack;a feed tube supported by the main plate and extending into the stack;an end cap coupled to the stack for defining an anode air stream plenum in fluid communication with the anodes;an inner cylinder supported by and sealingly attached to the main plate such that the inner cylinder at least partially surrounds the stack to define a cathode air stream plenum in fluid communication with the cathodes, wherein the exhaust plenum is in fluid communication with the anode air stream plenum and cathode air stream plenum;an insulation cap coupled to the main plate to define a flame space with the main plate;a CPOX reactor in the flame space; andan outer cylinder depending from the insulation cap and at least partially surrounding the inner cylinder to define an annular exhaust gap for exhaust gas from the exhaust plenum. 5. A solid oxide fuel cell system as recited in claim 4, wherein the inner cylinder includes a step adjacent the main plate to define a portion of the cathode air stream plenum. 6. A solid oxide fuel cell system as recited in claim 4, wherein the main plate is planar and substantially circular. 7. A solid oxide fuel cell system comprising: a stack;a feed tube extending through the stack for providing an anode feed stream;a main plate secured to the stack and forming an exhaust plenum therewith, the main plate also defining at least one feed hole;an inner cylinder coupled to the main plate and enclosing the stack to form a cathode feed plenum for a cathode air stream, and a cathode exhaust flow into the exhaust plenum;a hot zone boundary element connected to the main plate and having: i) a cap defining a flame space with the main plate; ii) a first stage of a tail gas combustor located in the flame space, wherein the exhaust flow enters the flame space by the at least one feed hole and, in turn, passes through the first stage to become a first stage exhaust stream; iii) an outer cylinder coupled to the cap and enclosing the inner cylinder to define an annular exhaust gap around the inner cylinder, wherein the annular exhaust gap is in fluid communication with the flame space so that the first stage exhaust stream cools therein to provide heat to the cathode air stream; and iv) a second stage of the tail gas combustor located in the annular exhaust gap, wherein the cooled first stage exhaust stream passes through the second stage for further combustion before exiting. 8. A solid oxide fuel cell system having an improved hot zone comprising: a stack fixed between an inlet end tube sheet and an outlet end tube sheet;an end cap sealed to the inlet end tube sheet to form an anode feed plenum;a main plate coupled to the outlet end tube sheet to form an exhaust plenum;a feed tube supported by the main plate and extending centrally through the inlet end tube sheet and outlet end tube sheet, the feed tube having a CPOX reactor configured so that flow from the CPOX reactor is directed into the stack via the anode feed plenum and heat from the CPOX reactor radiates to the stack;a partial cylinder depending from the main plate around a portion of the stack;an intermediate cylinder having a closed end and an open end, the open end being attached to the main plate such that the intermediate cylinder defines an annular feed gap around the partial cylinder for containing a cathode air stream;an insulation cap coupled to the main plate for forming a flame space in communication with the exhaust plenum; andan outer cylinder having a closed end and an open end, the open end being coupled to the main plate such that the outer cylinder defines an exhaust annular gap around the intermediate cylinder for containing hot exhaust gases exiting the flame space, wherein heat is transferred from the hot exhaust gases to the cathode air stream. 9. A solid oxide fuel cell system as recited in claim 8, wherein the main plate supports the stack and forms a seal with the insulation cap. 10. A solid oxide fuel cell system as recited in claim 8, wherein the main plate forms a seal with the intermediate cylinder. 11. A solid oxide fuel cell system as recited in claim 8, further comprising a tail gas combustor fixed in the flame space to receive cathode and anode exhaust gases that pass through an exit hole defined in the main plate, wherein exhaust from the tail gas combustor is directed into the exhaust annular gap. 12. A solid oxide fuel cell system as recited in claim 11, wherein the tail gas combustor has a first stage in the flame space and a second stage in the exhaust annular gap. 13. A solid oxide fuel cell system comprising: a stack having an anode feed plenum for receiving an anode feed stream;a main plate supporting the stack and defining an exhaust plenum;an inner cylinder having a closed end and an open end, the open end being attached to the main plate such that the inner cylinder defines a cathode feed plenum for containing a cathode air stream;an outer cylinder having a closed end and an open end, the open end being attached to the main plate such that the outer cylinder defines an exhaust annular gap around the inner cylinder, the exhaust annular gap being in fluid communication with the exhaust plenum, wherein a heat exchanger is formed between the inner and outer cylinders; andmeans in fluid communication with the stack for mixing the cathode air stream and anode air stream to create an exhaust gas, and directing the exhaust gas into the exhaust annular gap, wherein the means includes holes defined in the main plate, an inlet end tube sheet disposed in the inner cylinder and an outlet end tube sheet disposed in the inner cylinder, wherein the stack is fixed between the inlet end tube sheet and the outlet end tube sheet. 14. A solid oxide fuel cell system as recited in claim 13, further comprising: an end cap sealed to the inlet end tube sheet to form the anode feed plenum; anda feed tube extending centrally through the inlet end tube sheet and outlet end tube sheet, the feed tube having a CPOX reactor so that flow from the CPOX reactor is directed into the stack and heat from the CPOX reactor is delivered to the stack. 15. A solid oxide fuel cell system as recited in claim 14, wherein the CPOX reactor is in a location selected from the group consisting of outside the stack, well within the stack, and near an end of the stack. 16. A solid oxide fuel cell system as recited in claim 13, wherein the stack has tubular cells, each cell having an anode located at an inside surface and a cathode located on an outside surface. 17. A solid oxide fuel cell system as recited in claim 13, further comprising an open-ended two-layer shell depending from the main plate, the two-layer shell having a feed tube extending into the stack, and inner and outer tubular portions such that a service space is created between the inner and outer tubular portions, wherein the outer tubular portion nestles closely within the inner cylinder and, as a result, a heat exchanger with high heat transfer is formed there between. 18. A solid oxide fuel cell system as recited in claim 17, wherein the feed tube acts as a power lead for an electrical device. 19. A solid oxide fuel cell system as recited in claim 1, further comprising: a recuperator, wherein the tail gas combustor includes a first combustion stage and a second catalytic stage, and wherein the recuperator operates between the first combustion stage and the second catalytic stage for transferring heat from the exhaust gas before the exhaust gas enters the second catalytic stage. 20. A solid oxide fuel cell system as recited in claim 19, wherein the heat is transferred to a cathode air feed stream, the first combustion stage includes an igniter, and the solid oxide fuel cell system is portable. 21. A solid oxide fuel cell system as recited in claim 19, further comprising: a feed tube supported by the main plate and extending centrally through the stack, the feed tube having a CPOX reactor configured so that flow from the CPOX reactor is directed into the stack via the anode feed plenum and heat from the CPOX reactor radiates to the stack. 22. A solid oxide fuel cell system as recited in claim 1, wherein the tail gas combustor comprises: a combustion stage for receiving a mixture of anode and cathode exhaust gas to create a combustion stage exhaust; anda catalytic stage are arranged such that the combustion stage exhaust cools before entering the catalytic stage to prevent vaporizing a noble metal in the catalytic stage. 23. A solid oxide fuel cell system as recited in claim 22, wherein the tail gas combustor further comprises: a recuperator for cooling the combustion stage exhaust by transferring heat to a cathode air feed stream.