Ultra-high efficiency turbine and fuel cell combination

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ULTRA-HIGH EFFICIENCY TUBRINE AND FUEL CELL COMBINATION 2TEK CORPORATIONC:23326

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ULTRA-HIGH EFFICIENCY TURBINEAND FUEL CELL COMBINATION

Background of the Invention5

This invention relates to gas or steam turbines, and specifically to highperformance power systems employing such devices.

Conventional high performance gas turbine power systems exist and are10 known. Prior gas turbine power systems include a compressor, a combustor, and a mechanical turbine, typically connected in-line, e.g., connected along the same axis. In aconventional gas turbine, air enters the compressor and exits at a desirable elevated pressure.This high-pressure air stream enters the combustor, where it reacts with fuel, and is heated toa selected elevated temperature. This heated gas stream then enters the gas turbine and 15 expands adiabatically, thereby performing work. One deficiency of gas turbines of thisgeneral type is that the turbine typically operates at relatively low system efficiencies, forexample, around 25%, with systems of megawatt capacity.

One prior art method employed to overcome this problem is to employ a 20 recuperator for recovering heat. This recovered heat is typically used to further heat the airstream prior to the stream entering the combustor. Typically,*he recuperator improves thesystem efficiency of the gas turbine upwards to about 30%. A drawback of this solution isthat the recuperator is relatively expensive and thus greatly adds to the overall cost of thepower system. 25

Another prior art method employed is to operate the system at a relatively highpressure and a relatively high temperature to thereby increase system efficiency. However,the actual increase in system efficiency has been nominal, while the system is subjected to thecosts associated with the high temperature and pressure mechanical components. 30

Still another prior art method utilized by plants having power capacities above100 MW is to thermally couple the high temperature exhaust of the turbine with a heatrecovery steam generator for a combined gas turbine/steam turbine application. Thiscombined cycle application typically improves the system operating efficiency upwards to 35 about 55%. However, this efficiency is still relatively low.

Thus, there exists a need in the art for high performance power systems. Inparticular, an improved gas turbine power system that is capable of integrating andemploying the desirable properties of electrochemical converters would represent a major -2- improvement in the industry. More particularly, an integrated electrochemical converter andgas turbine system that reduces the costs associated with providing dedicated thermalprocessing systems while significantly increasing the overall system power efficiency wouldalso represent a major improvement in the art.

Summary of the Invention

The present invention provides for a power system that integrates anelectrochemical converter with a gas turbine. The electrochemical converter and gas turbineconstitute a relatively highly efficient power system, e.g., efficiency about 70%, for theproduction of electricity. /

The gas turbine power system of the present invention includes a compressorfor compressing a first medium, and an electrochemical converter in fluid communicationwith the compressor and adapted to receive the first medium and a second medium. Theconverter is configured to allow an electrochemical reaction between the first and secondmediums, thereby producing exhaust having a selected elevated temperature. The powersystem further includes a turbine in fluid communication with the electrochemical converterand adapted to receive the converter exhaust, such that the turbine converts theelectrochemical converter exhaust into rotary motion for electric power generation. ο

According to one aspect of the invention, the power system further includes agenerator which receives the rotary energy of the turbine, and which produces electricity inresponse to the turbine rotary energy. The electrochemical converter is preferably adapted tooperate at an elevated temperature and at various pressures.

According to another aspect, the power system further incudes a heatexchanger element, in thermal association with the electrochemical converter, for extractingwaste heat from the converter exhaust and for transferring the waste heat to the turbine.

According to still another aspect, the electrochemical converter includes aninternal heating element that internally heats the first and second medium to the converteroperating temperature. The converter is composed of, in another aspect, a plurality of planaror tubular converter elements which include a circular electrolyte layer having an oxidizerelectrode material on one side and a fuel electrode material on the opposing side.

According to another aspect, the electrochemical converter includes anelectrochemical converter assembly having a plurality of stacked converter elements which -3- include a plurality of electrolyte plates having an oxidizer electrode material on one side anda fuel electrode material on the opposing side, and a plurality of interconnector plates forproviding electrical contact with the electrolyte plates, such that the stack of converterelements is assembled by alternately stacking interconnector plates with the electrolyte plate.In another aspect, the stacked converter elements further include a plurality of manifoldsaxially associated with the stack and adapted to receive the first and second mediums, and amedium heating element, associated with the manifolds, for heating at least a portion of thefirst and second mediums to the converter operating temperature.

According to yet another aspect, the interconnector plate is a thermallyconductive connector plate, and the medium heating element includes a thermally conductiveand integrally formed extended surface, integrally formed with the interconnector plate, andwhich protrudes into the axial manifolds. In another embodiment, the stack of converterelements includes a plurality of spacer plates interposed between the electrolyte plates and theinterconnector plates, and the medium heating element includes a thermally conductive andintegrally formed extended surface of the spacer plate that protrudes into the plurality of axialmanifolds.

According to one practice of the invention, the electrochemical converter assembly generates waste heat which heats the first and second mediums to the converter operating temperature, and which is conductively transferred to the first and second mediums by the interconnector plate. *

According to another aspect, the power system further includes a preheatingelement for preheating the first and second mediums prior to introduction to theelectrochemical converter. The preheating element is preferably either an externalregenerative heat exchanger or a radiative heat exchanger. According to another practice ofthe invention, either the medium heating element or the preheating element can be utilized todisassociate the first and second mediums, which includes hydrocarbons and reformingagents, into non-complex reaction species.

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According to another aspect of the invention, the power system furtherincludes a converter exhaust heating element, in communication with the electrochemicalconverter and the turbine, for heating the exhaust of the converter to a selected elevatedtemperature prior to introduction to the turbine. According to one practice of the invention,the heating element heats the converter exhaust to a temperature higher than the converterexhaust temperature. The exhaust heating element is preferably a natural gas combustor.

The power system can further include a regenerative thermal enclosure element which formsa pressure vessel about the electrochemical converter. -4- 115,649/2

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The invention further provides for a steam turbine power system that includesan electrochemical converter for producing exhaust and waste heat having a selected elevatedtemperature, a steam generator associated with the electrochemical converter, and a turbineassociated with the steam generator and configured for producing electricity. US Patent No.5,501,781

According to one aspect, the steam turbine power system includes a heatexchanger element for radiatively exchanging heat between the converter and the steamgenerator.

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According to another aspect, the power system further includes a heatrecovery heat exchanger, associated with the turbine, that receives the converter exhaust andconvectively transfers waste heat from the converter exhaust to the turbine. 15 According to another aspect, the electrochemical converter includes an electrochemical converter assembly having a plurality of stacked converter elements whichinclude a plurality of electrolyte plates having an oxidizer electrode material on one side anda fuel electrode material on the opposing side, and a plurality of interconnector plates forproviding electrical contact with the electrolyte-plates., The stack of converter elements is 20 assembled by alternately stacking interconnector plates with the electrolyte plate.

According to another aspect, the stacked converter elements further includes aplurality of manifolds axially associated with the stack and adapted to receive reactants, and areactant heating element, associated with the manifolds, for heating at least a portion of the 25 reactants to the converter operating temperature. According to one practice, the interconnector plate includes a thermally conductive connector plate, and the reactant heatingelement includes a thermally conductive and integrally formed extended surface of theinterconnector plate that protrudes into the plurality of axial manifolds. 30 In yet another aspect, the stack of converter elements further includes a plurality of spacer plates interposed between the electrolyte plates and the interconnectorplates.

According to another aspect, the reactant heating element includes a thermally 35 conductive and integrally formed extended surface of the spacer plate that protrudes into theplurality of axial manifolds.

According to one practice of the invention, the electrochemical converterassembly generates waste heat which heats the reactants to the converter operating 115,649/2 -5- US Patent No. temperature. This waste heat is conductively transferred to the reactants by the5,501,781 interconnector plate.

In another aspect, the steam turbine power system further includes a5 preheating element for preheating the reactants prior to introduction to the electrochemical converter. The preheating element can include an external regenerative heat exchanger or aradiative heat exchanger.

According to another practice, either or both the preheating element or the '10 reactant heating element disassociates the reactants, which includes hydrocarbons andreforming agents, into non-complex reaction species.

The invention further provides for a power system that includes anelectrochemical converter adapted to receive input reactants and to produce waste heat and 15 exhaust, and a gas turbine that includes a compressor and a mechanical turbine that producesexhaust having a selected elevated temperature. The system further includes a steamgenerator that receives the gas turbine exhaust and that radiatively couples the exhaust of thegas turbine to a working medium. The system also includes a steam turbine that is associatedwith at least the steam generator and that is adapted to receive the working medium. 20

The invention further provides for a power system that includes anelectrochemical converter adapted to receive input reactants and to produce waste heat andexhaust, and a gas turbine that includes a compressor and a mechanical turbine that producesexhaust having a selected elevated temperature. The system further includes a steam 25 generator that receives the gas turbine exhaust and that convectively couples the exhaust ofthe gas turbine to a working medium. The system also includes a steam turbine that isassociated with the steam generator and that is adapted to receive the working medium.According to one practice, power is generated by the electrochemical converter, the steamturbine, and the gas turbine. 30

Brief Description of the Drawings

The foregoing and other objects, features and advantages of the invention will 35 be apparent from the following description and apparent from the accompanying drawings, inwhich like reference characters refer to the same parts throughout the different views. Thedrawings illustrate principles of the invention and, although not to scale, show relativedimensions. 115,649$ -6- FIG. 1 is a schematic block diagram of a power system employing an·.·. electrochemical converter serially in-line with a gas turbine according to the present invention: 5 FIG. 2 is a schematic block diagram of an alternate embodiment of a power system employing an electrochemical converter out of line with a gas turbine according to thepresent invention; zX FIG. 3 is a schematic block diagram of a power system employing an10 electrochemical converter and a steam turbine according to the present invention; 20

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FIG. 4 is a schematic block diagram of another embodiment of a power systememploying both a gas turbine, a steam turbine, and a converter exhaust heating elementaccording to the present invention: FIG. 5 is a plan view, partially cut-away, of a pressure vessel enclosing aseries of electrochemical converters of the present invention; FIG. 6 is a perspective view of a basic cell unit of an electrochemicalconverter of the invention: FIG. 7 is a perspective view of an alternate embodiment of the basic cell unitof the electrochemical converter of the present invention: and FIG. S is a cross-sectional view of the cell unit of FIG. 6; FIG. 9 is a schematic view of a multi-shaft gas turbine power systememploying an electrochemical converter according to the present invention: and FIG. 10 graphically illustrates the combined power system efficiency of thepower system of the present invention. -7- 115,649/2^

Description of Illustrated Embodiments 10 15 FIG. 1 shows a gas turbine power system according to the present invention.The illustrated in-line, aero-derivative gas turbine power system 70 includes anelectrochemical converter 72 and a gas turbine assembly. The gas turbine comprises acompressor 76, a turbine 80, and a generator 84. Air from air source 73 is introduced to thecompressor 76 by way of any suitable conduit where it is compressed, and thus heated, andthen discharged and introduced to the electrochemical converter 72. The .fuel 74 isintroduced to a preheater 68 where it is preheated to a selected elevated temperature belowthe converter operating temperature. The heated air and fuel function as input reactants andpower the electrochemical converter 72.

The converter 72 heats ±e compressed air introduced by the compressor 76and the fuel 74 to produce high temperature exhaust. The exhaust is introduced to the gasturbine 80, which converts this thermal energy into rotary energy, for subsequent transfer toan electric generator 84.J Specifically, the turbine converts the high temperature exhaust intorotary motion (via a turbine shaft), which performs work for electric power generation. {TheUS Patent No. generator 84 produces electricity that can be used for both commercial and residential5,501,7p purposes.} One benefit of utilizing the electrochemical converter as the gas turbine combustor20 is that the converter functions as an additional electric generator. {The illustrated electricalUS Patent No connections 88A and 88B show that electricity can be extracted from both the generator 845,501,781 and the converter 72.j The gas turbine components ,and generator are art known and commercially available. Those of ordinary skill will readily understand the operation of thegas turbine components, as well as the integration of the electrochemical converter and the25 gas turbine, especially in light of the present description and illustrations. For example, theordinarily skilled artisan will readily recognize that the converter 72 can either fully orpartially replace the combustor of the. gas turbine of the present invention. FIG. 2 illustrates a power system 90 where the electrochemical converter 72' is30 coupled off-line from the gas turbine. Air from the air source 73' is compressed by the compressor 76', discharged, and then introduced to the off-line converter 72'. Fuel from aό fuel source 74' is introduced to the converter and the air and fuel are consumed thereby. The £ oo converter thermally disassociates the fuel into constituent non-complex reaction species, je © typically H2 and CO, and creates high temperature exhaust. The exhaust is introduced to the ’'T 35 gas turbine 80' which is coupled to the electric generator 84'. The illustrated generator 84'and converter 72' can be used to power the illustrated propulsion motor 86. The system 90can further employ a preheater, similar to the preheater of FIG. 1, to preheat the reactantsprior to introduction to the converter 72. 115,649/2 -8- 10 FIG. 3 illustrates a power system 95 that employs an electrochemicalconverter 72", a heat recovery steam generator 108 (HRSG), and a steam turbine 112,connected as shown. The steam generator 108 functions as a preheater by preheating theinput reactants, e.g., air ahd fuel, to a desirable elevated temperature below the operatingtemperature of the converter 72". The convener utilizes the input reactants and creates wasteheat and heated exhaust 91. The exhaust 91 can be conveyed to the steam generator 108 byany suitable means, such as by a fluid conduit. The heated exhaust helps preheat thereactants 73,74 by a regenerative heat exchange process, while concomitantly heating theworking medium typically associated with the steam turbine, such as water, to produce steamfor the steam turbine 112. In an alternate embodiment, the steam generator 108 includesinternally a reformer for reforming fuel by thermal disassociation, which typically involvesthe reformation of hydrocarbons and reforming agents into non-complex reaction species. US Patent No.- 5,501,781 FIG. 4 shows an alternate power system 100 that utilizes an electrochemical 15 converter, a gas turbine, and a steam turbine,, The illustrated power system 100 includes asecondary combustor 104, a steam generator 108', and a steam turbine 112'. Fuel from a fuelsource 74 and water 102 for reforming, generally supplied by a fluid reservoir (not shown),are introduced to the electrochemical converter 72". The water 102 and the waste heatproduced by the converter 72" help reform the input fuel, e.g., fossil fuel, into usable non- 20 complex reaction species, e.g.. such as molecular hydrogen and carbon monoxide. Air fromthe air source 73 is preferably introduced to the converter 72" by way of the compressor orblower 76" and combines with the input fuel to power the converter 72"·. The converter 72"produces a high temperature exhaust, typically around 1000cC, which is further heated to a-selected elevated temperature, e.g., 1300°C, by the secondary combustor 104 to match the 25 predetermined inlet temperature requirements of the gas turbine 80". The gas turbine produces an exhaust output 81 which is passed through a heat recovery steam generator 108’for subsequent use with the bottoming steam turbine 1121 The steam turbine output iscoupled to the electric generator 84" which produces electricity. Electrical connections 88A'and 8SB' indicate that electricity can be directly extracted from both the electrochemical 30 converter 72" and the generator 84".

The illustrated power systems of FIGS. 1-4 provide the advantage in that theyallow electricity to be produced in an high efficiency system by the direct integration of ahighly efficient, compact electrochemical converter with the bottoming plant constituent 35 components. The integration of the electrochemical converter with a gas turbine in themanner illustrated in FIGS. 1-4 produces agas turbine power system that has an overallpower efficiency of about 70° ό. This system efficiency represents a significant increase overthe efficiencies achieved by prior art gas turbine systems and prior art electrochemicalsystems alone. The illustrated gas turbine power systems incorporate an electrochemical 115,649/2 -9-

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Oct. 17, 1995 converter to provide high grade thermal energy and electricity, while utilizing the benefits ofelectrochemical converters. For example, the converter operates as a low NOx thermalsource, thereby improving environmental performance relative to conventional gas turbinegenerating plants.

The high system efficiency of the combined electrochemical converter and gasturbine system is graphically illustrated in FIG. 10. The ordinate axis of the graph denotesthe overall system efficiency in percent and the abscissa denotes the power ratio of the hybridsystem. The power ratio is defined as the quotient of the sum of the sizes of theelectrochemical converter and the gas turbine (FC + GT) divided by the size of the gasturbine (GT). Graph line 200 illustrates that the overall system efficiency can exceed 60%when utilizing a fuel cell having an efficiency of 50% and a gas turbine having an efficiencyof 25%. Likewise, graph line 210 illustrates that the overall system efficiency can exceed60% when utilizing a fuel cell having an efficiency of 55% and a gas turbine having anefficiency of 35%, and depending upon the power ratio, can approach 70%. The graph lines200 and 210 also illustrate that the sizes and efficiencies of the electrochemical converter andgas turbine can be selected to maximize the overall system efficiency. Additionally, thegraphs illustrate that a correspondingly large increase in system efficiency occurs when a gasturbine is combined with an electrochemical converter: a result that was heretofore unknown.For example, as previously stated, the gas turbine power system employing an electrochemical converter has an overall system efficiency exceeding 60% and approaching70%. depending upon the sizes and efficiencies of the constituent gas turbine and theelectrochemical converter. ί 25 FIG. 9 is a schematic representation of a power system 300 that integrates an electrochemical converter with a multiple-shaft gas turbine system. The illustrated gas ; turbine system can be a conventional combustion turbine system. The illustrated hybrid i system 300 includes a pair of compressors C1 and C2. a pair of turbines TI and T2. a i generator 305. an intercooler 310. and one or more electrochemical converters 320. A pair ot 30 shafts 322.324 connect turbine TI and T2 to mechanical compressors Cl and C2.respectively.

As shown, air from an air inlet enters the compressor Cl at its inlet and iscompressed thereby. The compressed air then exits the compressor at its outlet and enters 35 intercooler 310. which reduces the temperature of the compressed air prior to the air exitingthe intercooler. The intercooler 3 10 receives a cooling fluid, such as water, at its inlet from afluid source (not shown) and discharges the water at its outlet.

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The cooled, compressed air then enters compressor C2. which againcompresses the air prior to introduction to the first electrochemical convener 320. The air istransferred between the convener 320 and compressor C2 along fluid pathway 328. The air.upon introduction to the convener, reacts with fuel from a fuel source (not shown) and are —---—--- - ...... ι consumed by the electrochemical convener 320 to generate electricity.

The convener exhaust is introduced to the turbine T2 along fluid pathway 330.the exhaust of which is introduced to a secondary convener 320. The secondary convener ·generates electricity and reheats the exhaust prior to introduction to turbine TI. The exhaustof the turbine Tl is preferably carried away from the system 300 along fluid pathway 332 forsubsequent use. The rotary energy of the turbine Tl is preferably divided between themechanical compressor Cl via the power shaft assembly 322 and the electric generator 305.The generator 305 can be used to generate electricity for a variety· of residential andcommercial purposes. Although the illustrated system 300 employs a pair of electrochemicalconveners 320. those of ordinary skill will recognize that only one convener may be used,with the other convener being replaced by a conventional combustor.

Other variations of the above designs exist and are deemed to be within thepurview of one of ordinary skill. For example, a series of gas turbine assemblies may be 20 employed, or any number of compressors, combustors and turbines may be used. The presentinvention is further intended to encompass the integration of an electrochemical converterwith most types of gas turbines, including, single-shaft gas turbines, double-shaft gasturbines, regenerative gas turbines, iniercooled gas turbines, and reheat gas turbines. In itsbroadest aspect, the present invention encompasses a hybrid power system that combines an 25 electrochemical converter and a conventional gas turbine. According to one preferredpractice of the invention, the converter replaces, either fully or partially, one or morecombustors of the gas turbine power system. o

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The direct integration of an electrochemical converter with a gas turbine isaided when the electrochemical converter 72 is housed within a high pressure vessel 120. Apreferred type of converter encasement is illustrated in FIG. 5. where a pressure vessel 120.which also functions as a regenerative thermal enclosure, encases a series oi stacked fuel cellassemblies 122. which are described in greater detail below. The-pressure vessel 120includes an exhaust outlet manifold 124. electrical connectors 126 and input reactantmanifolds 12S and 130. In a preferred embodiment, the oxidizer reactant is introduced to theresident fuel cell assemblies through the centrally located manifolds 130. and the fuel reactantis introduced through the fuel manifolds 128 located about the periphery of the v essel 120. 115,649/3 -11-

As described above, the electrochemical converter can be operated at an ' elevated temperature and at either ambient pressure or at an elevated pressure. Theelectrochemical converter is preferably a fuel cell system that can Include an Interdigitatedheat exchanger, similar to the type shown and described in U.S. Patent No. 4,853,100, whichis herein incorporated by reference.

Fuel cells typically disassociate fuel by utilizing the chemical potential ofselected fuel species, such as hydrogen or carbon monoxide molecules, to produce oxidizedmolecules in addition to electrical power. Since the cost of supplying molecular hydrogen orcarbon monoxide is relatively higher than providing traditional fossil fuels, a fuel processingor reforming step can be utilized to convert the fossil fuels, such as coal and natural gas, to areactant gas mixture high in hydrogen and carbon monoxide. Consequently, a fuel processor,either dedicated or disposed internally within the fuel cell, is employedjo reform, by the useof steam, oxygen, or carbon dioxide (in an endothermic reaction), the fossil fuels into non-complex reactant gases.

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10 US Patent No5,501,781 15 FIGS. 6-8 illustrate the basic cell unit 10 of the electrochemical converter 72,which is particularly suitable for integration with conventional gas turbines. The cell unit 10includes an electrolyte plate 20 and an interconnector plate 30. In one embodiment, the 20 electrolyte plate 20 can be made of a ceramic, such as a stabilized zirconia material

ZrCb(Y2O3)’ on which a porous oxidizer electrode material 20A and a porous fuel electrodematerial 20B are disposed thereon. Exemplary materials for the oxidizer electrode materialare perovskite materials, such as LaMnOjCSr). Exemplary materials for the fuel electrodematerial are cermets such as ZrCb/Ni and ZrCb/NiO. 25

The interconnector plate 30 preferably is made of an electrically and thermallyconductive interconnect material. Examples of such material include nickel alloys, platinumalloys, non-metal conductors such as silicon carbide. La(Mn)CrO3. and preferablycommercially available Inconel, manufactured by Inco., U.S.A. The interconnector plate 30 30 serves as the electric connector between adjacent electrolyte plates and as a partition betweenthe fuel and oxidizer reactants. As best shown in FIG.fc. the interconnector plate 30 has acentral aperture 32 and a set of intermediate, concentric radially outwardly spaced apertures34. A third outer set of apertures 36 are disposed along the outer cylindrical portion orperiphery of the plate 30. 35 . ...

The interconnector plate 30 has a textured surface 38. The textured surfacepreferably has formed thereon a series of dimples 40, as shown in FIG. 8, which form a seriesof connecting reactant-flow passageways. Preferably, both sides of the interconnector plate30 have the dimpled surface formed thereon. Although the intermediate and outer set of 115,649/2 US Patent No.5,501,781 - _______ -12- apertures 34 and 36, respectively, are shown with a selected number of apertures, those ofordinary skill will recognize that any number of apertures or distribution patterns can beemployed, depending upon the system and reactant-flow requirements. 5 Likewise, the electrolyte plate 20 has a central aperture 22, and a set of intermediate and outer apertures 24 and 26 that are formed at locations complementary to theapertures 32, 34 and 36, respectively, of the interconnector plate 30.

Referring to FIG. 7, a spacer plate 50 can be interposed between the10 electrolyte plate 20 and the interconnector plate 30. The spacer plate 50 preferably has a corrugated surface 52 that forms a series of connecting reactant-flow passageways, similar tothe interconnecting plate 30. The spacer plate 50 also has a number of concentric apertures54, 56, and 58 that are at locations complementary to the apertures of the interconnect andelectrolyte plates, as shown. Further, in this arrangement, the interconnector plate 30 is 15 devoid of reactant-flow passageways. The spacer plate 50 is preferably made of anelectrically conductive material, such as nickel.

The illustrated electrolyte plates 20, interconnector plates 30, and spacer plates50 can have any desirable geometric configuration. Furthermore, the plates having the 20 illustrated manifolds can extend outwardly in repetitive or non-repetitive patterns, and thusare shown in dashed lines.

Referring to FIG. 8, when the electrolyte plates 20 and the interconnectorplates 30 are alternately stacked and aligned along their respective apertures, the apertures 25 form axial (with respect to the stack) manifolds that feed the cell unit with the input reactantsand that exhaust spent fuel. In particular, the aligned central apertures 22,32,22' form inputoxidizer manifold 17, the aligned concentric apertures 24,34,24' form input fuel manifold 18,and the aligned outer apertures 26,36,26' form spent fuel manifold 19. 30 The dimpled surface 38 of the interconnector plate 30 has, in the cross- sectional view of FIG. 8, a substantially corrugated pattern formed on both sides. Thiscorrugated pattern forms the reactant-flow passageways that channel the input reactantstowards the periphery of the interconnector plates. The interconnector plate also has anextended heating surface or lip structure that extends within each axial manifold and about 35 the periphery of the interconnector plate. Specifically, the interconnector plate 30 has a flatannular extended surface 31A formed along its outer peripheral edge. In a preferredembodiment, the illustrated heating surface 31A extends beyond the outer peripheral edge ofthe electrolyte plate 20. The interconnector plate further has an extended heating surface thatextends within the axial manifolds, for example, edge 3IB extends into and is housed within 115,649/2 -13-

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the axial manifold 19; edge 31C extends into and is housed within the axial manifold 18; andedge 3 ID extends into and is housed within the axial manifold 17. The extended heatingsurfaces can be integrally formed with the interconnector plate or can be coupled or attachedthereto. The heating surface need not be made of the same material as the interconnectorplate, but can comprise any suitable thermally conductive material that is capable ofwithstanding the operating temperature of the electrochemical converter. In an alternateembodiment, the extended heating surface can be integrally formed with or coupled to thespacer plate. US Patent No. - 5,501,781 — 10 The absence of a ridge or other raised structure at the interconnector plate periphery provides for exhaust ports that communicate with the external environment. Thereactant-flow passageways connect, fluidwise, the input reactant manifolds with the outerperiphery, thus allowing the reactants to be exhausted to the external environment, or to .athermal container or pressure vessel disposed about the electrochemical converter, FIG. 5. 15

Referring again to FIG. 8, the illustrated sealer material 60 can be applied toportions of the interconnector plate 30 at the manifold junctions, thus allowing selectively aparticular input reactant to flow across the interconnector surface and across the matingsurface of the electrolyte plate 20. The interconnector plate bottom 3 0B contacts the fuel 20 electrode coating 20B of the electrolyte plate 20. In this arrangement, it is desirable that thesealer material only allow fuel reactant to enter the reactant-flow passageway, and thuscontact the fuel electrode. ....

As illustrated, the sealer material 60A is disposed about the input oxidizer 25 manifold 17, forming an effective reactant flow barrier about the oxidizer manifold 17. Thesealer material helps maintain the integrity of the fuel reactant contacting the fuel electrodeside 20B of the electrolyte plate 20, as well as maintain the integrity of the spent fuel , exhausted through the spent fuel manifold 19.

30 The top 30A of the interconnector plate 30 has the sealer material 60B disposed about the fuel input manifolds 18 and the spent fuel manifold 19. The top of theinterconnector plate 30A contacts the oxidizer coating 20B' of an opposing electrolyte plate20'. Consequently, the junction at the input oxidizer manifold 17 is devoid of sealer material,thereby allowing the oxidizer reactant to enter the reactant-flow passageways. The sealer 35 material 60B that completely surrounds the fuel manifolds 18 inhibits the excessive leakageof the fuel reactant into the reactant-flow passageways, thus inhibiting the mixture of the fueland oxidizer reactants. Similarly, the sealer material 60C that completely surrounds the spentfuel manifold 19 inhibits the flow of spent oxidizer reactant into the spent fuel manifold 19.Hence, the purity of the spent fuel that is pumped through the manifold 19 is maintained. 115,649/2 -14- us Patent No.*5,501,781

Referring again to FIG. 8, the oxidizer reactant can be introduced to theelectrochemical converter through axial manifold 17 that is formed by the apertures 22, 32,and 22' of the electrolyte and interconnector plates, respectively. The oxidizer is distributed 5 over the top of the interconnector plate 30A, and over the oxidizer electrode surface 20A1 bythe reactant-flow passageways. The spent oxidizer then flows radially outward toward theperipheral edge 31 A, and is finally discharged along the converter element periphery. Thesealer material 60C inhibits the flow of oxidizer into the spent fuel manifold 19. The flowpath of the oxidizer through the axial manifolds is depicted by solid black arrows 26A, and 10 through the oxidizer cell unit by the solid black arrows 26B.

The fuel reactant is introduced to the electrochemical converter 10 by way offuel manifold 18 formed by the aligned apertures 24, 34, and 24' of the plates. The fuel isintroduced to the reactant-flow passageways and is distributed over the bottom of the 15 interconnector plate 30B, and over the fuel electrode coating 20B of the electrolyte plate 20.Concomitantly, the sealer material 60A prevents the input oxidizer reactant from entering thereactant-flow passageways and thus mixing with the pure fuel/spent fuel reactant mixture.The absence of any sealer material at the spent fuel manifold 19 allows spent fuel to enter themanifold 19. The fuel is subsequently discharged along the annular edge 31A of the 20 interconnector plate 30. The flow path of the fuel reactant is illustrated by the solid blackarrows 26C.

The dimples 40 of the interconnector surface have an apex 40A that contactthe electrolyte plates, in assembly, to establish an electrical connection therebetween. 25 A wide variety of conductive materials can be used for the thinelectroconnector plates of this invention. Such materials should meet the followingrequirements: (1) high strength, as well as electrical and thermal conductivity; (2) goodoxidation resistance up to the working temperature; (3) chemical compatibility and stability 30 with the input reactants; and (4) manufacturing economy when formed into the textured plateconfiguration exemplified by reactant-flow passageways.

The suitable materials for interconnector fabrication include nickel alloys,nickel-chromium alloys, nickel-chromium-iron alloys, iron-chromium-aluminum alloys, 35 platinum alloys, cermets of such alloys and refractory material such as zirconia or alumina,silicon carbide and molybdenum disilicide.

The textured patterns of the top and bottom of the interconnector plate can beobtained, for example, by stamping the metallic alloy sheets with one or more sets of

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US Patent No,’ 5,501,781 10 matched male and female dies. The dies are preferably prefabricated according to the desiredconfiguration of the interconnector plate, and can be hardened by'heat treatment to withstandthe repetitive compressing actions and mass productions, as well as the high operatingtemperatures. The stamp forming process for the interconnectors is preferably conducted inmultiple steps due to the geometrical complexity of the gas passage networks, e.g., thedimpled interconnector plate surface. The manifolds formed in the interconnector plates arepreferably punched out at the final step. Temperature annealing is recommended between theconsecutive steps to prevent the overstressing of sheet material. The stamping method iscapable of producing articles of varied and complex geometry while maintaining uniformmaterial thickness.

Alternatively, corrugated interconnectors can be formed by electro-depositionon an initially flat metal plate using a set of suitable masks. Silicon carbide interconnectorplates can be formed by vapor deposition onto pre-shaped substrates, by sintering of bonded 15 powders, or by self-bonding processes.

The oxidizer and fuel reactants are preferably preheated to a suitabletemperature prior to entering the electrochemical converter. This preheating can beperformed by any suitable heating structure, such as a regenerative heat exchanger or a 20 radiative heat exchanger, for heating the reactants to a temperature sufficient to reduce theamount of thermal stress applied to the converter. A significant feature of the present invention is that the hybrid power systemsillustrated in FIGS 1-4 and 9 unexpectedly operate at system efficiencies that exceed any 25 that were previously known. Another significant feature of the present invention is that theextended heating surfaces 3 ID and 31C heat the reactants contained within the oxidizer andfuel manifolds 17 and 18 to the operating temperature of the converter. Specifically, theextended surface 3ID that protrudes into the oxidizer manifold 17 heats the oxidizer reactant. .and the extended surface 31C that protrudes into the fuel manifold 18 heats the fuel reactant. 30 The highly thermally conductive interconnector plate 30 facilitates heating of the input reactants by conductivelv transferring heat from the fuel cell internal surface, e.g.. the middleregion of the conductive inter'connector plate, to the extended surfaces or lip portions, thusheating the input reactants to the operating temperature prior to traveling through reactantflow passageways. The extended surfaces thus function as a heat fin. This reactant heating 35 structure provides a compact converter that is capable of being integrated with an electricitygenerating power system, and further provides a highly efficient system that is relatively low-in cost. Electrochemical converters incorporating fuel cell components constructed accordingto these principles and employed in conjunction with a gas turbine provides a power systemhaving a relatively simple system configuration. ϋ 5,649/2 -16- US Patent No.5,501,781

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The operating temperature of the electrochemical converter is preferablybetween about 20°C and 1500°C, and the preferred fuel cell types employed by the presentinvention are solid oxide fuel cells, molten carbonate fuel cells, alkaline fuel cells, phosphoricacid fuel cells, and proton membrane fuel cells.

In an alternate embodiment, the electrolyte and interconnector plates can havea substantially tubular shape and have an oxidizer electrode material disposed on one side anda fuel electrode material disposed on the opposing side. The plates can then be stacked 10 together in a like manner.

It will thus be seen that the invention contains improvements over the priorart. Since certain changes may be made in the above constructions without departing fromthe scope of the invention, it is intended that all matter contained in the above description or 15 shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are to cover all genericand specific features of the invention described herein, and all statements of the scope of theinvention which, as a matter of language, might be said to fall therebetween. For example, 20 the electrochemical converter employing the interconnector plate edge extensions of thepresent invention can also employ molten carbonate, phosphoric acid, alkaline and protonexchange membrane electrochemical converters and other like converters.

What is claimed is: 25