Made available in DSpace on 2014-12-17T14:07:01Z (GMT). No. of bitstreams: 1 SamaraMV_DISSERT.pdf: 3021267 bytes, checksum: 443b2ba79e877562b95c18cd66a9716c (MD5) Previous issue date: 2012-03-22 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Cells the solid oxide fuel are systems capable to directly convert energy of a chemical reaction into electric energy in clean, quiet way and if its components in the solid state differentiate of excessively the techniques for having all. Its more common geometric configurations are: the tubular one and to glide. Geometry to glide beyond the usual components (anode, cathode and electrolyte) needs interconnect and sealant. E the search for materials adjusted for these components is currently the biggest challenge found for the production of the cells. The sealants need to present chemical stability in high temperatures, to provoke electric isolation, to have coefficient of compatible thermal expansion with the excessively component ones. For presenting these characteristics the glass-ceramics materials are recommended for the application. In this work the study of the partial substitution of the ZrO2 for the Al2O3 in system LZS became it aiming at the formation of system LZAS, this with the addition of natural spodumene with 10, 20 and 30% in mass. The compositions had been casting to a temperature of 1500?C and later quickly cooled with the objective to continue amorphous. Each composition was worn out for attainment of a dust with average diameter of approximately 3?m and characterized by the techniques of DRX, FRX, MEV, dilatometric analysis and particle size analysis. Later the samples had been conformed and treated thermally with temperatures in the interval between 700-1000 ?C, with platform of 10 minutes and 1 hour. The analyses for the treated samples had been: dilatometric analysis, DRX, FRX, electrical conductivity and tack. The results point with respect to the viability of the use of system LZAS for use as sealant a time that had presented good results as isolating electric, they had adhered to a material with similar ? of the components of a SOFC and had presented steady crystalline phases / Pilhas a combust?vel de ?xido s?lido (PaCOS) s?o sistemas capazes de converter energia de uma rea??o qu?mica diretamente em energia el?trica de maneira limpa, silenciosa e se diferenciam das demais t?cnicas por ter todos os seus componentes no estado s?lido. Suas configura??es geom?tricas mais comuns s?o: a tubular e a planar. A geometria planar al?m dos componentes usuais (anodo, catodo e eletr?lito) necessita de interconectores e selantes. E a busca por materiais adequados para esses componentes ? atualmente o maior desafio encontrado para a produ??o das pilhas. Os selantes precisam apresentar estabilidade qu?mica em altas temperaturas, provocar isolamento el?trico e ter coeficiente de dilata??o t?rmica compat?vel com os demais componentes. Por apresentarem essas caracter?sticas os materiais vitrocer?micos s?o os mais recomendados para a aplica??o. Neste trabalho fez-se o estudo da substitui??o parcial da Zr02 pela Al2O3 no sistema LZS visando a forma??o do sistema LZAS, isso com a adi??o 10, 20 e 30% em massa de espodum?nio natural. As composi??es foram fundidas a uma temperatura de 1500?C e depois resfriadas rapidamente com o objetivo de continuarem amorfas. Cada composi??o foi mo?da para obten??o de um p? com di?metro m?dio de aproximadamente 3?m e caracterizada pelas t?cnicas de DRX, FRX, MEV, dilatometria e granulometria. Posteriormente as amostras foram preparadas por compacta??o e tratadas termicamente com temperaturas no intervalo entre 700-1000 ?C, com patamar de 10min e 1h. As an?lises para as amostras tratadas foram: dilatometria, DRX, FRX, condutividade el?trica e ader?ncia. Os resultados apontam para a viabilidade do sistema LZAS para uso como selante uma vez que apresentaram bons resultados como isolante el?trico, aderiram a um material com coeficiente de dilata??o t?rmica (?) semelhante a dos componentes de uma PaCOS e apresentaram fases cristalinas est?veis / 2020-01-01

Made available in DSpace on 2014-12-17T14:07:09Z (GMT). No. of bitstreams: 1 AmandaLM_DISSERT.pdf: 3676559 bytes, checksum: 256cb3ce22bbf3b5f114a2ff3021de96 (MD5) Previous issue date: 2013-02-06 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Fuel cells are electrochemical devices that convert chemical energy into electricity. Due to the development of new materials, fuel cells are emerging as generating clean energy generator. Among the types of fuel cells, categorized according to the electrode type, the solid oxide fuel cells (SOFC) stand out due to be the only device entirely made of solid particles. Beyond that, their operation temperature is relatively high (between 500 and 1000 ?C), allowing them to operate with high efficiency. Another aspect that promotes the use of SOFC over other cells is their ability to operate with different fuels. The CeO2 based materials doped with rare earth (TR+3) may be used as alternatives to traditional NiO-YSZ anodes as they have higher ionic conductivity and smaller ohmic losses compared to YSZ, and can operate at lower temperatures (500-800?C). In the composition of the anode, the concentration of NiO, acting as a catalyst in YSZ provides high electrical conductivity and high electrochemical activity of reactions, providing internal reform in the cell. In this work compounds of NiO - Ce1-xEuxO2-δ (x = 0.1, 0.2 and 0.3) were synthesized from polymeric precursor, Pechini, method of combustion and also by microwave-assisted hydrothermal method. The materials were characterized by the techniques of TG, TPR, XRD and FEG-SEM. The refinement of data obtained by X-ray diffraction showed that all powders of NiO - Cex-1EuxO2-δ crystallized in a cubic phase with fluorite structure, and also the presence of Ni. Through the characterizations can be proved that all routes of preparation used were effective for producing ceramics with characteristics suitable for application as SOFC anodes, but the microwave-assisted hydrothermal method showed a significant reduction in the average grain size and improved control of the compositions of the phases / C?lulas a combust?vel s?o dispositivos eletroqu?micos que convertem a energia qu?mica em el?trica. Em virtude do desenvolvimento de novos materiais, as c?lulas a combust?vel v?m se destacando como promissores na gera??o de energia de forma limpa. Dentre os tipos de c?lulas a combust?vel, classificadas de acordo com o tipo de eletr?lito, destacam-se as de ?xido s?lido (SOFC), por serem as ?nicas inteiramente constitu?das por s?lidos. Al?m disso, pela sua temperatura de opera??o ser relativamente elevada (entre 500 e 1000 ?C), estas c?lulas operam com alta efici?ncia. Outro aspecto que favorece o emprego de SOFC ? a sua habilidade de operar com diferentes combust?veis, como fontes de hidrog?nio.Os materiais a base de CeO2 dopados com terras raras (TR+3) podem ser utilizados como alternativas aos tradicionais anodos de NiO-YSZ. Al?m de maior condutividade i?nica maior e menores perdas ?hmicas, elas podem operar a temperaturas mais baixas (500- 800?C). Na composi??o do anodo, a concentra??o de NiO, atuando como catalisador confere alta condutividade el?trica e alta atividade eletroqu?mica das rea??es, proporcionando a reforma interna do combust?vel na c?lula. Neste trabalho compostos de NiO - Ce1-xEuxO2-δ (x = 0,1; 0,2 e 0,3), foram sintetizados a partir do m?todo dos precursores polim?ricos, Pechini, do m?todo de combust?o e, tamb?m, pelo m?todo hidrotermal assistido por micro-ondas. Os materiais obtidos foram caracterizados atrav?s das t?cnicas de TG, DRX, TPR e MEV-FEG. O refinamento dos dados obtidos pela difra??o de raios X indicou que todos os p?s de NiO - Ce1- xEuxO2-δ cristalizaram-se em uma fase c?bica com estrutura fluorita, e tamb?m a presen?a de NiO. Todas as rotas de prepara??o utilizadas mostraram-se eficientes para a produ??o de p?s com caracter?sticas adequadas para aplica??o como anodos de SOFC, por?m o m?todo hidrotermal assistido por micro-ondas apresentou significativa redu??o do tamanho m?dio de gr?os e melhor controle das composi??es das fases

Made available in DSpace on 2014-12-17T14:58:15Z (GMT). No. of bitstreams: 1 LaureniaMPG_DISSERT.pdf: 2747629 bytes, checksum: a8b9f0209bf9acabd46832a08265ed7f (MD5) Previous issue date: 2012-05-08 / The lanthanum strontium cobalt iron oxide (La1-xSrxCo1-yFeyO3 LSCF) is the most commonly used material for application as cathode in Solid Oxide Fuel Cells (SOFCs), mainly due to their high mixed ionic electronic conductivity between 600 and 800?C. In this study, LSCF powders with different compositions were synthesized via a combination between citrate and hydrothermal methods. As-prepared powders were calcined from 700 to 900?C and then characterized by X-ray fluorescence, X-ray diffraction, thermal analyses, particle size analyses, nitrogen adsorption (BET) and scanning electronic microscopy. Films of composition La0,6Sr0,4Co0,2Fe0,8O3 (LSCF6428), powders calcined at 900?C, were screen-printed on gadolinium doped ceria (CGO) substrates and sintered between 1150 and 1200?C. The effects of level of sintering on the microstructure and electrochemical performance of electrodes were evaluated by scanning electronic microscopy and impedance spectroscopy. Area specific resistance (ASR) exhibited strong relation with the microstructure of the electrodes. The best electrochemical performance (0.18 ohm.cm2 at 800?C) was obtained for the cathode sintered at 1200?C for 2 h. The electrochemical activity can be further improved through surface activation by impregnation with PrOx, in this case the electrode area specific resistance decreases to values as low as 0.12 ohm.cm2 (800?C), 0.17 ohm.cm2 (750?C) and 0.31 ohm.cm2 (700?C). The results indicate that the citrate-hydrothermal method is suitable for the attainment of LSCF particulates with potential application as cathode component in intermediate temperature solid oxide fuel cells (IT-SOFCs) / A cobaltita de lant?nio dopada com estr?ncio e ferro (La1-xSrxCo1-yFeyO3 LSCF) ? comumente o material mais utilizado para aplica??o como catodo em c?lula a combust?vel de ?xido s?lido (SOFC), principalmente devido a sua elevada condutividade mista i?nica e eletr?nica entre 600 e 800?C. Neste trabalho, p?s de LSCF de diferentes composi??es foram sintetizados via uma combina??o entre os m?todos citrato e hidrotermal. Os p?s como obtidos foram calcinados entre 700 e 900 ?C e caracterizados por fluoresc?ncia de raios X, difratometria de raios X, an?lises t?rmicas, distribui??o de tamanho de part?cula, adsor??o gasosa (BET) e microscopia eletr?nica de varredura. Filmes de composi??o La0,6Sr0,4Co0,2Fe0,8O3 (LSCF6428) foram obtidos por serigrafia de p?s calcinados a 900?C. Os filmes foram depositados sobre substratos de c?ria dopada com gadol?nia (CGO) e ent?o sinterizados entre 1150 e 1200?C. Os efeitos do patamar de sinteriza??o na microestrutura e no desempenho eletroqu?mico dos eletrodos foram avaliados por microscopia eletr?nica de varredura e espectroscopia de imped?ncia. A resist?ncia espec?fica por ?rea apresentou forte rela??o com a microestrutura dos eletrodos. O melhor desempenho eletroqu?mico (0,18 ohm.cm2 a 800?C) foi obtido para o catodo sinterizado a 1200?C por 2 horas. A atividade eletroqu?mica pode ainda ser melhorada mediante ativa??o superficial por impregna??o com PrOx, neste caso a resist?ncia espec?fica por ?rea do eletrodo diminui para valores t?o baixos como 0,12 ohm.cm2 (800?C), 0,17 ohm.cm2 (750?C) e 0,31 ohm.cm2 (700?C). Os resultados obtidos indicam que o m?todo citrato-hidrotermal ? adequado para a prepara??o de particulados de LSCF com potencial aplica??o como catodo em c?lulas a combust?vel de ?xido s?lido de temperatura intermedi?ria (600-800?C)

Células a combustível de óxido sólido suportadas no eletrólito de zircônia estabilizada com ítria (YSZ) foram fabricadas usando a técnica do recobrimento por rotação (spin-coating) para deposição de catodos de manganita de lantânio dopada com estrôncio (LSM) e anodos compósitos de níquel e YSZ (Ni-YSZ). Parâmetros microestruturais dos eletrodos, tais como espessura, tamanho médio de partículas e temperatura de sinterização foram otimizados, visando reduzir a resistência de polarização da célula e melhorar o seu desempenho. Estes estudos serviram de base para a fabricação de células com camada catalítica para uso com etanol direto. Sobre o anodo Ni-YSZ da célula foi depositada uma camada catalítica de céria dopada com gadolínia (CGO) com 0,1% em peso de irídio (Ir-CGO). A camada catalítica visa reformar o etanol antes do seu contato com o anodo Ni-YSZ, evitando o depósito de carbono na superfície do Ni que inviabiliza o uso de combustíveis primários contendo carbono nestas células a combustível. Inicialmente, a célula a combustível foi testada com etanol e as melhores condições de operação foram determinadas. Em seguida, as células unitárias foram testadas com etanol sem adição de água por períodos de tempo de até 390 horas. As células a combustível a etanol direto com camada catalítica operam no modo de reforma interna gradual, apresentando boa estabilidade e densidades de corrente similares às obtidas na operação com hidrogênio. Após a operação das células a combustível a etanol direto, análises de microscopia eletrônica de varredura mostraram que não houve formação significativa de depósitos de carbono na superfície do Ni, indicando que a camada catalítica de Ir-CGO foi efetiva para operação com o etanol. Testes de células a combustível a etanol direto sem a camada catalítica revelaram uma rápida degradação nas horas iniciais de operação com formação de grandes quantidades de depósitos de carbono identificados visualmente. Considerando-se a operação estável com etanol a seco por tempos relativamente longos de operação, os resultados alcançados representam um avanço significativo e apontam para o desenvolvimento de células a combustível a etanol direto usando-se os componentes tradicionais com a adição de uma camada catalítica. / Yttria-stabilized zirconia (YSZ) electrolyte supported solid oxide fuel cells were fabricated with spin-coated strontium-doped lanthanum manganite (LSM) cathodes and Ni-YSZ cermet anodes. The microstructural parameters of the electrodes such as thickness, average particle size, and sintering temperature were optimized to decrease the polarization resistance of the single cells and to improve their electrochemical performance. These preliminar studies provided the basis for the fabrication of single fuel cells with a catalytic layer of gadolinia-doped ceria (CGO) and 0.1 wt% iridium (Ir-CGO) deposited onto the anode. The catalytic layer aims at the stable operation with dry (direct) ethanol; it avoids the contact of the alcohol with the anode, preventing the anode degradation by carbon deposition. Initially, the single cells were tested with ethanol and optimized operating parameters were determined. Then, the single cells were operated with anhydrous ethanol for periods of time up to 390 hours. The single cells with catalytic layer operate by the gradual internal reforming of ethanol, with good stability and delivering similar electric current densities as the ones measured using hydrogen as fuel. After single cell operation on direct ethanol, scanning electron microscopy analyses identified no significant carbon deposition on the surface of Ni, indicating that the Ir-CGO catalytic layer was effective for the reforming of ethanol. Such results were compared to the ones of standard single cells operating on dry ethanol, which showed a fast degradation and the formation of large amounts of carbon deposits. Considering the rather stable performance of single cells running on dry ethanol for relatively long times, such results represent a significant advance towards the development of direct ethanol solid oxide fuel cells using the standard components and a catalytic layer.

La pile à combustible Solid Oxide Fuel Cell (PAC-SOFC) est un système de production d’énergie « propre » qui permet de convertir de l’hydrogène en énergie électrique en ne rejetant que de l’eau. Une nouvelle configuration appelée « monochambre » semble être particulièrement attrayante compte tenu de ces nombreux avantages sur la configuration bi-chambre classique : simplification de fabrication, baisse de la température de fonctionnement, utilisation d’hydrocarbures comme combustible… La mise en place d’un tel système implique le développement de nouveaux matériaux d’électrodes satisfaisants à de nouveaux critères. L’évaluation en condition réaliste de 7 matériaux de cathode potentiels par diverses caractérisations structurale, texturale et catalytique à mis en évidence la difficulté de développer un matériau possédant toutes les caractéristiques requises. Ainsi, un matériau présentant le meilleur compromis est proposé. Une bibliothèque de 15 catalyseurs supportés (3 métaux et 5 supports différents) a ensuite été développée. Ces catalyseurs, ayant pour but d’être intégrés dans l’anode de la pile pour réaliser le reformage d’hydrocarbures, ont été évalués selon une approche combinatoire en condition réaliste (présence d’hydrocarbure, d’eau, de dioxyde de carbone), ce qui a permis de sélectionner les catalyseurs imprégnés de platine, plus robuste notamment en présence d’eau. Finalement, le couplage de la spectroscopie d’impédance avec la chromatographie en phase gaz a permis d’évaluer le comportement électrochimique d’une nouvelle architecture anodique comportant un catalyseur issu de la bibliothèque. Les tests ont montré que l’ajout d’un catalyseur est bénéfique pour la diminution des résistances de polarisation anodiques par production localisée d’hydrogène à partir d’hydrocarbure. / Solid Oxide Fuel Cell is a device for “clean” electricity production from chemical energy. The new configuration called “single-chamber” seems to be very attractive with several advantages over bi-chamber conventional configuration: easier manufacturing, lowering of working temperature, possible use of hydrocarbons as fuel… Such configuration involves the development of new electrode materials satisfying new requirements. The evaluation of 7 potential cathode materials through several characterizations has shown that a compromise has to be found since one material does not exhibit all the requested features. A library of 15 supported catalysts (3 metals and 5 supports) was developed. These catalysts, aimed at be located inside the anodic cermet, were evaluated through a combinatorial approach in realistic condition (presence of hydrocarbon, water, carbon dioxide). Platinum-based catalysts are found the most robust, especially in presence of water. Finally, innovative coupling of electrochemical impedance spectroscopy with gas chromatography measurements was carried out to characterise a new anodic architecture with an enclosed Pt-based catalyst previously evaluated. Tests revealed the beneficial effect of the catalyst insertion over anodic polarisation resistance by hydrogen production from hydrocarbon.

Planare keramische Hochtemperaturbrennstoffzellen liefern aufgrund ihres hohen Wirkungsgrades sowie einer hohen Variabilität geeigneter Brennstoffe einen wertvollen Beitrag zur ressourcenschonenden Stromproduktion. Für einen sicheren Betrieb dieser Brennstoffzellen sind hermetisch dichte und elektrisch isolierende Dichtungen unabdingbar. Aufgrund ihrer chemischen Stabilität sowie der Anpassung relevanter Fügeeigenschaften wie Viskosität und thermischem Ausdehnungsverhalten eignen sich insbesondere teilkristalline Glaslote als Dichtungs- und Fügewerkstoffe für diese Aufgabe. Für einen zuverlässigen Langzeitbetrieb von Brennstoffzellensystemen ist neben der Anpassung der Fügeparameter ein umfassendes Verständnis der Alterungsprozesse von Glasloten im Fügeverbund unter Betriebsbedingungen hinsichtlich Gasdichtheit und elektrischem Iso-lationsvermögen von entscheidender Bedeutung. In grundlegenden Untersuchungen zeigt diese Arbeit auf, welche vielschichtigen Degradationsprozesse in teilkristallinen Glasloten unter simulierten Einsatzbedingungen ablau-fen. Durch geeignete Versuchsabläufe gelang es, diese Einflüsse hinsichtlich ihrer Auswirkungen auf Degradationsprozesse zu separieren und zu bewerten. Die daraus gewonnenen Erkenntnisse flossen in eine Glaslotentwicklung ein, mit der die Degradationsstabilität teilkristalliner Glaslote unter den gegebenen Einsatzbedingungen deutlich erhöht werden konnte. Besondere Berücksichtigung fand hierbei der Einfluss der Glaszusammensetzung auf Degradationsprozesse im Verbund mit den metallischen Fügepartnern sowie die Porenbildung in gesinterten glaskeramischen Gefügen unter brennstoffzellentypischen Betriebsbedingungen. Im Gesamtergebnis zeigt die vorliegende Arbeit, dass zur Erfüllung von Fügeaufgaben neben der Anpassung intrinsischer Glasloteigenschaften auch das langfristige Verhalten teilkristalliner Glaslote im Fügeverbund Berücksichtigung finden muss.:Einleitung Grundlagen von Brennstoffzellen Funktionsweise von Brennstoffzellen Einteilung von Brennstoffzellen Unterteilung keramischer Hochtemperaturbrennstoffzellen Planare Hochtemperaturbrennstoffzellen Aufbau und Werkstoffe Dichtungen für planare Hochtemperaturbrennstoffzellen Glimmerdichtungen Aktiv- und Reaktivlotdichtungen Glaslotdichtungen Verbunddichtungen Glaslotdichtungen in planaren Hochtemperaturbrennstoffzellen Eigenschaften von Glas und Glaskeramik Fügen keramischer Brennstoffzellenstapel mit Glasloten Degradation von Glasloten in SOFCs Stand der Technik – Literatur Motivation dieser Arbeit Material und Methoden Verwendetes Glaslotsystem Metallsubstrate Erhitzungsmikroskopie Dilatometrie Röntgenographische Phasenanalyse Qualitative Heißgasextraktion Chemische Analysen Ermittlung des elektrischen Widerstandes Versuchsaufbau kompakter Glasproben Versuchsaufbau für Auslagerung unter dualer Atmosphäre Ermittlung der Heliumleckrate Gefügeanalyse Ergebnisse und Diskussion Charakterisierung des Standardglaslotes S01 Auslagerung bei Verwendung inerter Elektroden an Luft Spannungsfreie Auslagerung zwischen Goldsubstraten Spannungsfreie Auslagerung zwischen Crofer 22 APU- und Gold-Substraten Auslagerung unter elektrischer Spannung, Kombination A: beide Elektroden aus Gold Auslagerung unter elektrischer Spannung, Kombination B: Anode Gold, Kathode Crofer 22 APU Auslagerung unter elektrischer Spannung, Kombination C: Anode Crofer 22 APU, Kathode Gold Auslagerung unter elektrischer Spannung, Kombination D: beide Elektroden aus Crofer 22 APU Auslagerungen unter relevanten Betriebsbedingungen Charakterisierung des Ausgangszustand des Gefüges Auslagerung unter dualer Atmosphäre ohne elektrische Spannung Auslagerung unter dualer Atmosphäre mit elektrischer Spannung Auswirkungen verzögerter elektrischer Spannung Beschleunigte Degradation durch erhöhte elektrische Spannung Langzeitauslagerungen unter dualer Atmosphäre Glaslotentwicklung für keramische Brennstoffzellen Mechanismen von Porenbildung im Glaslot Glaslote mit erhöhter Stabilität gegenüber Blasenbildung Erhöhung der Stabilität gegenüber metallischen Fügepartnern Untersuchung von Fügeeigenschaften ausgewählter Glaslote Auslagerungen neu entwickelter Glaszusammensetzungen Degradationsverhalten modifizierter ZnO-haltiger Glaslote Degradationsverhalten ZnO-freier Glaslote Zusammenfassung Ausblick Anhang Abkürzungen, Formelzeichen und Einheiten Abbildungsverzeichnis Tabellenverzeichnis Literaturverzeichnis

The potential of Solid Oxide Fuel Cell Gas Turbine (SOFC/GT) hybrid systems for fuel flexibility makes this technology greatly attractive for system hybridization with various fuel processing units in advanced power generation systems and/or polygeneration plants. Such hybrid technologies open up the possibility and opportunities for improvement of system reliabilities and operabilities. However, SOFC/GT hybrid systems have not yet reached their full potential in term of capitalizing on the synergistic benefits of fuel cell and gas turbine cycles. Integrating fuel cells with gas turbine and other components for transient operations increases the risk for exposure to rapid and significant changes in process dynamics and performance, which are primarily associated with fuel cell thermal management and compressor surge. This can lead to severe fuel cell failure, shaft overspeed, and gas turbine damage. Sufficient dynamic control architectures should be made to mitigate undesirable dynamic behaviours and/or system constraint violations before this technology can be commercialized. But, adequate understanding about dynamic coupling interactions between system components in the hybrid configuration is essential. Considering this critical need for system identification of SOFC/GT hybrid in fuel flexible systems, this thesis investigates the dynamic performance of SOFC/GT hybrid technology in response to fuel composition changes. Hardware-based simulations, which combined actual equipment of direct-fired recuperated gas turbine system and simulated fuel cell subsystem, are used to experimentally investigate the impacts of fuel composition changes on the SOFC/GT hybrid system, reducing potentially large inaccuracies in the dynamic study. The impacts of fuel composition in a closed loop operation using turbine speed control were first studied for the purpose of simplicity. Quantification of safe operating conditions for dynamic operations associated with carbon deposition and compressor stall and surge was done prior to the execution of experimentation. With closed loop tests, the dynamic performance of SOFC/GT hybrid technology due to a transition in gas composition could be uniquely characterized, eliminating the interactive effects of other process variables and disturbances. However, for an extensive system analysis, open loop tests (without turbine speed control) were also conducted such that potential coupling impacts exhibited by the SOFC/GT hybrid during fuel transients could be explored. Detailed characterization of SOFC/GT dynamic performance was performed to identify the interrelationship of each fuel cell variable in response to fuel composition dynamics and their contributions to operability of the system. As a result of lowering LHV content in the fuel feed, which involved a transition from coal-derived syngas to humidified methane composition in the SOFC anode, the system demonstrated a dramatic transient increase in fuel cell thermal effluent with a time scale of seconds, resulting from the conversion of fuel cell thermal energy storage into chemical energy. This transient was highly associated with the dynamics of solid and gas temperatures, heat flux, heat generation in the fuel cell due to perturbations in methane reforming, water-gas shifting, and electrochemical hydrogen oxidation. In turn, the dramatic changes in fuel cell thermal effluent resulting from the anode composition changes drove the turbine transients that caused significant cathode airflow fluctuations. This study revealed that the cathode air mass flow change was a major linking event during fuel composition changes in the SOFC/GT hybrid system. Both transients in cathode air mass flow and anode composition significantly affected the hybrid system performance. Due to significant coupling between fuel composition transitions and cathode air mass flow changes, thermal management of SOFC/GT hybrid systems might be challenging. Yet, it was suggested that modulating cathode air flow offered promise for effective dynamic control of SOFC/GT hybrid systems with fuel flexibility. / Thesis / Doctor of Philosophy (PhD)

No description available.

No description available.

No description available.