Neste trabalho estudou-se o efeito da granulometria do calcário na absorção de SO2 em batelada em reator de leito fluidizado borbulhante. Conversão e coeficiente global de reação foram estabelecidos a partir de condições simuladas, típicas de combustão em leito fluidizado. O sistema experimental foi constituído por um reator de 160 mm de diâmetro interno e altura de 450 mm. Utilizou-se granulometria estreita de dois tipos de calcários com diâmetros médios de 390, 462, 545, 650 e 770 &#956m. A areia de quartzo que compunha o leito tinha diâmetro igual ao do calcário. O ar foi aquecido por resistências elétricas e acrescido de frações de SO2, alcançado concentrações em torno de 1000 ppm. Os experimentos foram realizados com bateladas de 50 g de calcário, temperatura fixa de 850°C, e relação entre velocidades de fluidização e de mínima fluidização foi mantida 4/1. Os resultados mostram que a conversão variou entre 10 a 40% para o calcário magnesiano e 8 a 25% para o calcítico. O coeficiente global de taxa de reação aumentou com redução do diâmetro. O modelo de redução de dados não respondeu satisfatoriamente para partículas de 462 e 390 &#956m. / This work concerns the study of the effect of limestone particle size on S02 absorption in bench fluidized bed reactor plant. Conversion and global reaction rate coefficients were established for simulated conditions typical to fluidized bed combustion of coal. The reactor had an internal diameter of 160 mm and 450 high. The bed was fluidized with air containing a concentration of about 1000 ppm of S02. Narrows size distribution of two types of limestone with overage diameters of 390, 462, 545,650 and 770 mm. It were used sand of quartz that composed the bed had the same diameter of the limestone. The experiments were carried out on a batch mode introducing samples of 50 g limestone into the bed. The temperature of the process was fixed in 850ºC. The ration between gas fluidization velocity and minimum fluidization velocity was fixed about 4/1. The results show that the conversion varied among 10 to 40% for the magnesiano and 8 to 25% for the calcítico limestone. The global of reaction rate coefficient increased with reduction of diameter. The data reduction model did not answer satisfactorily for particles of 462 and 390 &#956m.

O principal objetivo deste trabalho foi obter parâmetros reativos para as reações de absorção de SO2 por calcários em leitos fluidizados e procurar correlacionar, através de dois modelos simples, os resultados obtidos para distribuições granulométricas amplas e estreitas. Foram estudadas cinco faixas estreitas, com diâmetros de 385, 460, 545, 650, 775 &#956m para dois tipos de calcários, um dolomítico (DP) e um calcítico (CI). A partir destas faixas estreitas foram compostas quatro misturas, com 498, 540, 543 e 617 &#956m. Um dos dois modelos foi usado para determinar a fração com que cada faixa estreita deveria estar presente na mistura. Uma das misturas, a Mistura 2 (540 &#956m), tinha distribuição de diâmetros aproximadamente normal e a outra, Mistura 3 (543 &#956m), distribuição plana. O leito, de 160 mm de diâmetro, foi fluidizado com ar à temperatura de 850ºC e utilizou areia como material particulado. O calcário foi introduzido em bateladas de 50 g em um leito de areia de mesmo diâmetro com cerca de 2,0 Kg de massa. Uma vazão de SO2 foi misturada ao ar antes que este entrasse no leito, de forma a resultar em uma concentração próxima à 1000 ppm na saída do reator. A concentração de saída foi monitorada e a sua queda, verificada após a introdução da batelada de calcário, foi utilizada em um modelo matemático para determinar os parâmetros reativos, entre eles a conversão, taxa de conversão e o coeficiente global de taxa de reação. Os modelos de distribuição granulométrica empregados produziram boa correlação entre as misturas e as faixas estreitas durante a sulfatação. Na calcinação, o processo mostrou-se mais lento para a distribuição ampla do calcário DP e não foi afetado para o CI. Em todos os casos estudados o diâmetro do calcário mostrou afetar significativamente e de forma inversa, a eficiência dos calcários na remoção do SO2. O calcário DP mostrou-se sempre mais eficiente do que o calcário CI. / The main objective of this work was to compare the reactivity of limestones with narrow and open particle size distribution in a bubling fluidized bed reactor and verify if the reactivity of the open sized mixtures could be predicted, using two simple models, from the known parameters of the narrow sized particles. Five narrow sizes were used, respectively 385, 460, 545, 650 and 775 &#956m for two different limestones, one calcitic (CI) and one Dolomitic (DP). Using this same material and one of the models, four mixtures were prepared with 498, 540, 543 and 617 &#956m of average diameter. The mixture of 540 &#956m had an aproximately normal distribution of sizes and the mixture of 543 &#956m a falt one. The bed, with 160 mm of diameter, was fluidized with air at a temperature of 850ºC, and 2 Kg of sand with the same size as the limestones, was used as the bed material. A flow of SO2 was mixed with the fluidization air prior to the gas distributor, producing a uniform concentration of about 1000 ppm at the reactor gas exaust. The limestone was then intoduced in a batch of 50 g and the SO2 concentration monitored. The change in the SO2 concentration after the limestone was intoduced in the reactor was used to derive the reactive parameters, namely the conversion, rate of conversion and global coefficient of reaction rate. The particle size distribution models produced a good correlation among the mixtures and the narrow sized particlesduring sulfatation. The calcination process was more slow for the open distribution of limestone DP but not affected for CI. In all cases there was a clear increase in the SO2 absorption as the particle size was reduced. Limestone DP was much more effective in the removal of SO2 than CI.

O principal objetivo deste trabalho foi obter parâmetros reativos para as reações de absorção de SO2 por calcários em leitos fluidizados e procurar correlacionar, através de dois modelos simples, os resultados obtidos para distribuições granulométricas amplas e estreitas. Foram estudadas cinco faixas estreitas, com diâmetros de 385, 460, 545, 650, 775 &#956m para dois tipos de calcários, um dolomítico (DP) e um calcítico (CI). A partir destas faixas estreitas foram compostas quatro misturas, com 498, 540, 543 e 617 &#956m. Um dos dois modelos foi usado para determinar a fração com que cada faixa estreita deveria estar presente na mistura. Uma das misturas, a Mistura 2 (540 &#956m), tinha distribuição de diâmetros aproximadamente normal e a outra, Mistura 3 (543 &#956m), distribuição plana. O leito, de 160 mm de diâmetro, foi fluidizado com ar à temperatura de 850ºC e utilizou areia como material particulado. O calcário foi introduzido em bateladas de 50 g em um leito de areia de mesmo diâmetro com cerca de 2,0 Kg de massa. Uma vazão de SO2 foi misturada ao ar antes que este entrasse no leito, de forma a resultar em uma concentração próxima à 1000 ppm na saída do reator. A concentração de saída foi monitorada e a sua queda, verificada após a introdução da batelada de calcário, foi utilizada em um modelo matemático para determinar os parâmetros reativos, entre eles a conversão, taxa de conversão e o coeficiente global de taxa de reação. Os modelos de distribuição granulométrica empregados produziram boa correlação entre as misturas e as faixas estreitas durante a sulfatação. Na calcinação, o processo mostrou-se mais lento para a distribuição ampla do calcário DP e não foi afetado para o CI. Em todos os casos estudados o diâmetro do calcário mostrou afetar significativamente e de forma inversa, a eficiência dos calcários na remoção do SO2. O calcário DP mostrou-se sempre mais eficiente do que o calcário CI. / The main objective of this work was to compare the reactivity of limestones with narrow and open particle size distribution in a bubling fluidized bed reactor and verify if the reactivity of the open sized mixtures could be predicted, using two simple models, from the known parameters of the narrow sized particles. Five narrow sizes were used, respectively 385, 460, 545, 650 and 775 &#956m for two different limestones, one calcitic (CI) and one Dolomitic (DP). Using this same material and one of the models, four mixtures were prepared with 498, 540, 543 and 617 &#956m of average diameter. The mixture of 540 &#956m had an aproximately normal distribution of sizes and the mixture of 543 &#956m a falt one. The bed, with 160 mm of diameter, was fluidized with air at a temperature of 850ºC, and 2 Kg of sand with the same size as the limestones, was used as the bed material. A flow of SO2 was mixed with the fluidization air prior to the gas distributor, producing a uniform concentration of about 1000 ppm at the reactor gas exaust. The limestone was then intoduced in a batch of 50 g and the SO2 concentration monitored. The change in the SO2 concentration after the limestone was intoduced in the reactor was used to derive the reactive parameters, namely the conversion, rate of conversion and global coefficient of reaction rate. The particle size distribution models produced a good correlation among the mixtures and the narrow sized particlesduring sulfatation. The calcination process was more slow for the open distribution of limestone DP but not affected for CI. In all cases there was a clear increase in the SO2 absorption as the particle size was reduced. Limestone DP was much more effective in the removal of SO2 than CI.

Abstract not available

Graduation date: 1998

L'étude des phénomènes fondamentaux de transport et de thermodynamique apparaissant lors de l'évaporation en milieu poreux permet l'investigation d'applications pratiques variées. Dans ce travail, nous développons des modèles fondamentaux d'évaporation en milieu poreux que nous appliquons ensuite au séchage en lit fluidisé de deux matériaux granulaires poreux : le PVC et la levure. Les modèles mis au point sont réalisés suivant une approche multiéchelle. Nous nous intéressons tout d'abord aux phénomènes se déroulant à l'échelle d'un pore. Les modèles développés à cette échelle sont ensuite exploités dans le cadre d'une étude à l'échelle d'un grain poreux. Le couplage des modèles de grain avec un modèle à l'échelle du réacteur permet alors l'étude des applications industrielles. A l'échelle du pore, nous étudions les phénomènes de transport dans un capillaire initialement rempli de liquide qui s'évapore vers l'atmosphère ambiante. L'objectif est de prédire le taux d'évaporation dans cette configuration. Nous nous intéressons successivement à la modélisation du transport de matière par convection-diffusion en phase gazeuse et la modélisation de l'impact de films liquides adsorbés à la paroi du capillaire sur le transport de matière. Ces deux modèles sont confrontés à des expériences d'évaporation en capillaires cylindriques visualisées à l'aide de deux dispositifs optiques. Le premier offre un suivi d'ensemble au cours du temps du capillaire, alors que le second, un interféromètre de Mach-Zehnder, permet une visualisation locale de la région entourant le ménisque. Le modèle portant sur le transport de matière par convection-diffusion mène à la définition d'un critère non dimensionnel permettant d'évaluer si la convection dans la phase gazeuse dans le capillaire doit être prise en compte pour évaluer le taux d'évaporation. Le modèle de film permet de prédire l'impact de celui-ci sur l'évaporation en présence d'un gaz inerte lorsque les mouvements convectifs en phase gazeuse sont négligeables. La confrontation de ce modèle avec les profils d'épaisseur des films obtenus à l'aide de interféromètre de Mach-Zehnder ne permet pas de valider le modèle, et ce, suite à une trop grande incertitude sur l'évaluation des interactions entre la paroi et le liquide. A l'échelle d'un grain, nous développons un modèle discret par réseau de pores et deux modèles continus pour tenter de prédire le taux d'évaporation et la distribution des phases dans le milieu poreux. Le modèle par réseau de pores prend en compte les transports de matière par diffusion en phase gazeuse, par convection dans les pores remplis de liquide et par convection dans les films liquides. Les effets visqueux en phase liquide sont également modelisés. Pour la prise en compte de ces derniers, nous montrons l'importance de l'usage d'un algorithme approprié. Nous évaluons ensuite au travers de trois nombres sans dimensions l'impact du transport par film et des effets visqueux sur l'évaporation et la distribution des phases. Cette analyse dimensionnelle est ensuite appliquée à l'étude de réseaux de pores pour lesquels la section des liaisons les constituant est idéalisée par des polygones réguliers. Pour les modèles continus après une vérification simplifiée de l'applicabilité de cette démarche, nous développons deux modèles simples. Dans les deux modèles, l'étape de séchage à vitesse constante est supposée limitée par le transport de matière externe au grain. Le premier modèle, dit à front pénétrant, suppose que l'étape de séchage à vitesse décroissante correspond à l'existence d'un front d'évaporation qui s'enfonce dans la matrice poreuse. Le second modèle, dit à surface d'échange variable, attribue cette même étape du séchage à une diminution progressive de la surface d'évaporation en surface du grain. A l'échelle du réacteur, nous présentons deux modèles visant à simuler deux types d'essais différents : le séchage en lit fluidisé et la thermogravimétrie analytique. Ces deux modèles sont couplés aux différents modèles à l'échelle de grain pour étudier le séchage de PVC et de levure tant en lit fluidisé que lors des essais de thermogravimétrie analytique. Dans le cas du PVC, le modèle par réseau de pores ne peut pas être appliqué de par la nécessité d'une trop grande puissance de calcul. Au niveau des modèles continus, nous montrons que l'application du modèle à surface d'échange variable permet de reproduire les courbes de séchage expérimentales des essais en lit fluidisé. Dans le cas de la levure, nous appliquons le modèle par réseau de pores et le modèle à front pénétrant. L'utilisation du modèle par réseau de pores nécessite une connaissance plus détaillée de la structure poreuse des grains. Le traitement d'une analyse par microtomographie nous permet d'obtenir un réseau de pores expérimental. Celui-ci est utilisé pour montrer que la méthode de caractérisation de la porosité par intrusion de mercure ne semble pas adaptée à un matériau deformable comme la levure. Le même réseau est utilisé pour simuler le séchage de grains de levure à l'aide du modèle par réseau de pores. Les simulations sont réalisées sur des réseaux équivalents à des coupes dans le solide. Le modèle par réseau de pores et le modèle à front pénétrant permettent tous deux de modéliser correctement le séchage de levure en lit fluidisé moyennant l'ajustement de leurs paramètres ajustables, respectivement la conductibilité des films liquide et la tortuosité. Pour l'essai de thermogravimétrie, ils ne parviennent à approcher que la première étape de celui-ci. Les avantages, défauts et complémentarités de ces deux modèles sont discutés. Nous évaluons ensuite l'impact du rétrécissement de la levure et des types d'eau sur le séchage de ce matériau. Le rétrécissement est, pour ce faire, mesuré à l'aide d'un stéréomicroscope. Ces premières mesures, exploratoires, mènent à la définition d'un modèle empirique de retrait du solide au cours de son séchage. En le prenant en compte dans les modèles déjà appliqués à la levure, nous montrons que le retrait a un impact significatif sur l'étape de séchage à vitesse décroissante. Cet impact peut cependant être masqué intégralement par la réévaluation des paramètres ajustables des différents modèles. Finalement, l'étude des types d'eau au travers d'un modèle simple appliqué à l'essai de thermogravimétrie analytique montre que les types d'eau ne doivent pas être pris en compte pour modéliser le séchage de levure. A l'issue de ce travail, nous disposons donc de modèles fondamentaux d'évaporation en milieu poreux. Ceux-ci peuvent être appliqués à des cas d'intérêt industriel, comme nous le réalisons pour le PVC et la levure. Ils peuvent servir à améliorer la compréhension de ces procédés. Ils représentent donc des outils de choix pour la conception, le dimensionnement et l'optimisation du séchage.

Production of hydrogen is primarily achieved via catalytic steam reforming, partial oxidation,and auto-thermal reforming of natural gas. Although these processes are mature technologies, they are somewhat complex and CO is formed as a by-product, therefore requiring a separation process if a pure or hydrogen-rich stream is needed. As an alternative method, supported metal catalysts can be used to catalytically decompose hydrocarbons to produce hydrogen. The process is known as catalytic cracking of hydrocarbons. Methane, the hydrocarbon containing the highest percentage of hydrogen, can be used in such a process to produce a hydrogen-rich stream. The decomposition of methane occurs on the surface of the active metal to produce hydrogen and filamentous carbon. As a result, only hydrogen is produced as a gaseous product, which eliminates the need of further separation processes to separate CO2 or CO. Nickel is commonly used in research as a catalyst for methane cracking in the 500-700C temperature range. To conduct methane catalytic cracking in a continuous manner, regeneration of the deactivated catalyst is required and circulation of the catalysts between cracking and regeneration cycles must be achieved. Different reactor designs have been successfully used in cyclic operation, such as a set of parallel fixed-bed reactors alternating between cracking and regeneration, but catalyst agglomeration due to carbon deposition may lead to blockage of the reactor and elevated pressure drop through the fixed bed. Also poor heat transfer in the fixed bed may lead to elevated temperature during the regeneration step when carbon is burned in air, which may cause catalyst sintering. A fluidized bed reactor appears as a viable option for methane catalytic cracking, since it would permit cyclic operation by moving the catalyst between a cracker and a regenerator. In addition, there is the possibility of using fine catalyst particles, which improves catalyst effectiveness. The aims of this project were 1) to develop and characterize a suitable nickel-based catalyst and 2) to develop a model for thermal catalytic decomposition of methane in a fluidized bed.

Fluidized bed is a suitable technology for combustion and gasification of biomass materials. Hydrodynamics occurring in the bed is crucial for the design and operation of the combustion or gasification unit. In the present study, hydrodynamic behavior of binary mixtures of biomass-silica sand in a bubbling fluidized bed was experimentally investigated. Five different biomass materials and silica sand with three different particle sizes were employed to form binary mixtures. Biomass materials were rice husk, sawdust, wheat straw, hazelnut shell and olive cake which are all potential energy sources for Turkey. Effects of mass percentage of biomass and particle size of silica sand on minimum fluidization velocity of the mixtures were determined. Comparisons between results of the present study and predictions of available correlations proposed for minimum fluidization velocity of binary mixtures were carried out. Mixing and segregation characteristics of biomass-silica sand binary mixtures were investigated for mixtures having different mass fraction of biomass and different silica sand particle sizes. Fluidization and bubbling behaviors of mentioned mixtures were observed in a 2-D fluidized bed and images taken during steady-state operation of bed were presented as visual tools to guide fluidization characteristics of the bed. Mass percentage increase of rice husk, wheat straw and sawdust resulted in increase in minimum fluidization velocity of the mixture whereas change in mass fraction of olive cake and hazelnut shell had no effect on minimum fluidization velocity. Minimum fluidization velocity increased with increase of silica sand particle size for all biomass-silica sand mixtures having same mass percentage of biomass. Vertical mixing pattern in the bed at steady state conditions were found almost same for all biomass-silica sand mixtures. Biomass acted as flotsam and accumulated mostly at the top of the bed and silica sand acted as jetsam and accumulated mostly at the bottom of the bed. 2-D bed experiments showed that mixing biomass materials with silica sand provides desired bubbling behavior in the bed.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xiv, 159 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 118-122).

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xiv, 137 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 106-109).