abstract: Emission of CO2 into the atmosphere has become an increasingly concerning issue as we progress into the 21st century Flue gas from coal-burning power plants accounts for 40% of all carbon dioxide emissions. The key to successful separation and sequestration is to separate CO2 directly from flue gas (10-15% CO2, 70% N2), which can range from a few hundred to as high as 1000°C. Conventional microporous membranes (carbons/silicas/zeolites) are capable of separating CO2 from N2 at low temperatures, but cannot achieve separation above 200°C. To overcome the limitations of microporous membranes, a novel ceramic-carbonate dual-phase membrane for high temperature CO2 separation was proposed. The membrane was synthesized from porous La0.6Sr0.4Co0.8Fe0.2O3-d (LSCF) supports and infiltrated with molten carbonate (Li2CO3/Na2CO3/K2CO3). The CO2 permeation mechanism involves a reaction between CO2 (gas phase) and O= (solid phase) to form CO3=, which is then transported through the molten carbonate (liquid phase) to achieve separation. The effects of membrane thickness, temperature and CO2 partial pressure were studied. Decreasing thickness from 3.0 to 0.375 mm led to higher fluxes at 900°C, ranging from 0.186 to 0.322 mL.min-1.cm-2 respectively. CO2 flux increased with temperature from 700 to 900°C. Activation energy for permeation was similar to that for oxygen ion conduction in LSCF. For partial pressures above 0.05 atm, the membrane exhibited a nearly constant flux. From these observations, it was determined that oxygen ion conductivity limits CO2 permeation and that the equilibrium oxygen vacancy concentration in LSCF is dependent on the partial pressure of CO2 in the gas phase. Finally, the dual-phase membrane was used as a membrane reactor. Separation at high temperatures can produce warm, highly concentrated streams of CO2 that could be used as a chemical feedstock for the synthesis of syngas (H2 + CO). Towards this, three different membrane reactor configurations were examined: 1) blank system, 2) LSCF catalyst and 3) 10% Ni/y-alumina catalyst. Performance increased in the order of blank system < LSCF catalyst < Ni/y-alumina catalyst. Favorable conditions for syngas production were high temperature (850°C), low sweep gas flow rate (10 mL.min-1) and high methane concentration (50%) using the Ni/y-alumina catalyst. / Dissertation/Thesis / Ph.D. Chemical Engineering 2011

Submitted by BENJAMIN KUNTE null (benjamin.kunte@gmail.com) on 2015-12-21T20:22:35Z No. of bitstreams: 1 Benjamin_Dissertation_Final_Version.pdf: 2440898 bytes, checksum: 129503961064a9371fbb24f9408bfbc6 (MD5) / Approved for entry into archive by Cássia Adriana de Sant ana Gatti (cgatti@marilia.unesp.br) on 2015-12-22T13:12:11Z (GMT) No. of bitstreams: 1 Benjamin_Dissertation_Final_Version.pdf: 2440898 bytes, checksum: 129503961064a9371fbb24f9408bfbc6 (MD5) / Made available in DSpace on 2015-12-22T13:12:11Z (GMT). No. of bitstreams: 1 Benjamin_Dissertation_Final_Version.pdf: 2440898 bytes, checksum: 129503961064a9371fbb24f9408bfbc6 (MD5) Previous issue date: 2015-12-18 / Os métodos mais promissores para reduzir gases de efeito estufa, bem como combater o iminente esgotamento das reservas de energia fóssil, são: a) o uso de combustíveis alternativos obtidos a partir da biomassa, como o biogás ou gás de síntese (syngas); b) o aumento da eficiência do sistema através da redução da percentagem de energia útil perdido para o ambiente. Enquanto a otimização da eficiência de uma determinada máquina da central elétrica, por exemplo, turbina a gás ou compressor, é um desenvolvimento muito demorado, a cogeração pode rápida e significativamente aumentar a eficiência global da central. Neste trabalho, análise termodinâmica, econômica e de emissões de um sistema de cogeração baseado em uma microturbina a gás de 200 kW combinado com uma caldeira de recuperação são conduzidas. Além disso, a operação de biogás e syngas é comparada com a operação de gás natural para investigar a pertinência destes dois combustíveis alternativos para o uso em micro turbinas a gás. A central de cogeração proposta mostrou-se tecnicamente viável para todos os combustíveis, porque a microturbina selecionada é disponível em várias versões, específicas para cada combustível, com sistemas de injeção de combustível otimizados. A central apresentou eficiências energéticas globais de 50,9%, 48,6% e 47,9% para operação com gás natural, biogás e syngas, respectivamente. Devido aos preços muito elevados do gás natural e do syngas, a central de cogeração apresentou viabilidade econômica apenas no caso de operação com biogás, com curtos períodos de retorno de aproximadamente 2,8 anos e alta economia anual esperada. Além disso, o biogás tem a maior eficiência ecológica e, portanto, apresentou-se como a melhor alternativa aos combustíveis fósseis. / The most promising methods to reduce greenhouse gases as well as counteract against the imminent depletion of fossil fuels are: a) the use of alternative fuels obtained from biomass, such as biogas or bio-syngas; b) enhancing the power plant efficiency by decreasing the percentage of useful energy lost to the environment. Whereas efficiency optimisation of a particular machine in a power plant, e.g. gas turbine or compressor, is a very longsome development, cogeneration can quickly and significantly increase the overall efficiency of a power plant. In this work, energetic, exergetic, emissions and economic analyses of a cogeneration system consisting of a 200 kW micro gas turbine combined with a heat recovery steam generator are introduced and conducted. Furthermore, biogas and syngas operation are compared to natural gas operation, to investigate the adequacy of these two alternative fuels for use in micro gas turbines. The proposed cogeneration plant proved to be technically feasible for all fuels, because the selected micro gas turbine Capstone C200 is available in various, fuel-specific versions with optimised fuel injection systems. The plant presented overall energetic efficiencies of 50.9%, 48.6% and 47.9% for natural gas, biogas and syngas operation, respectively. Due to very high natural gas and syngas prices, the cogeneration plant presented economic feasibility only in case of biogas operation, with short payback periods of approximately 2.8 years and high expected annual saving. Moreover, biogas has the highest ecologic efficiency and was therefore found to be the best alternative to fossil fuels.

Membranes are a promising, effective and energy efficient separation strategy for effluent gases in the Reverse Water Gas Shift (RWGS) reaction to increase the overall conversion of CO2 to CO. This process involves a separation and recycling process to reuse the unreacted CO2 from the RWGS reactor. The carbon monoxide produced from this reaction, alongside hydrogen (composing syngas), can be used in the Fischer-Tropsch process to create synthetic fuel, turning stationary CO2 emissions into a useable resource. A literature review was performed to select suitable polymers with high CO2 permeability and selectivities of CO2 over CO and H2. PDMS (polydimethylsiloxane) was selected and commercial and in-house PDMS membranes were tested. The highest CO2 permeability observed was 5,883 Barrers, including a CO2/H2 selectivity of 21 and a CO2/CO selectivity of 9, with ternary gas feeds. HY zeolite, silica gel and activated carbon were selected from previous research for their CO2 separation capabilities, to be investigated in PDMS mixed matrix membranes in 4 wt % loadings. Activated carbon in PDMS proved to be the best performing mixed matrix membrane with a CO2 permeability of 2,447 Barrers and comparable selectivities for CO2/H2 and CO2/CO of 14 and 9, respectively. It was believed that swelling, compaction and the homogeneity of the selective layer were responsible for trends in permeability with respect to driving force. The HY and silica gel mixed matrix PDMS membranes were believed to experience constraints in performance due to particle and polymer interfaces within the membrane matrix.

abstract: On average, our society generates ~0.5 ton of municipal solid waste per person annually. Biomass waste can be gasified to generate synthesis gas (syngas), a gas mixture consisting predominantly of CO, CO2, and H2. Syngas, rich in carbon and electrons, can fuel the metabolism of carboxidotrophs, anaerobic microorganisms that metabolize CO (a toxic pollutant) and produce biofuels (H2, ethanol) and commodity chemicals (acetate and other fatty acids). Despite the attempts for commercialization of syngas fermentation by several companies, the metabolic processes involved in CO and syngas metabolism are not well understood. This dissertation aims to contribute to the understanding of CO and syngas fermentation by uncovering key microorganisms and understanding their metabolism. For this, microbiology and molecular biology techniques were combined with analytical chemistry analyses and deep sequencing techniques. First, environments where CO is commonly detected, including the seafloor, volcanic sand, and sewage sludge, were explored to identify potential carboxidotrophs. Since carboxidotrophs from sludge consumed CO 1000 faster than those in nature, mesophilic sludge was used as inoculum to enrich for CO- and syngas- metabolizing microbes. Two carboxidotrophs were isolated from this culture: an acetate/ethanol-producer 99% phylogenetically similar to Acetobacterium wieringae and a novel H2-producer, Pleomorphomonas carboxidotrophicus sp. nov. Comparison of CO and syngas fermentation by the CO-enriched culture and the isolates suggested mixed-culture syngas fermentation as a better alternative to ferment CO-rich gases. Advantages of mixed cultures included complete consumption of H2 and CO2 (along with CO), flexibility under different syngas compositions, functional redundancy (for acetate production) and high ethanol production after providing a continuous supply of electrons. Lastly, dilute ethanol solutions, typical of syngas fermentation processes, were upgraded to medium-chain fatty acids (MCFA), biofuel precursors, through the continuous addition of CO. In these bioreactors, methanogens were inhibited and Peptostreptococcaceae and Lachnospiraceae spp. most likely partnered with carboxidotrophs for MCFA production. These results reveal novel microorganisms capable of effectively consuming an atmospheric pollutant, shed light on the interplay between syngas components, microbial communities, and metabolites produced, and support mixed-culture syngas fermentation for the production of a wide variety of biofuels and commodity chemicals. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2017

Orientador: Caio Glauco Sanchez / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-13T05:14:36Z (GMT). No. of bitstreams: 1 Figueiredo_FlavioAugustoBueno_D.pdf: 4083626 bytes, checksum: 203f07dd538191c353f5988fc849f84e (MD5) Previous issue date: 2009 / Resumo: Os processos de gaseificação e pirólise sofrem grande influência do tipo de biomassa que está sendo utilizada propiciando variações na distribuição dos produtos (alcatrão, cinzas, água, gás). No processo de gaseificação é obtido, principalmente, um gás combustível que pode variar seu poder calorífico de acordo com as temperaturas e agentes gaseificantes utilizados. A biomassa utilizada neste trabalho é a casca de castanha de caju proveniente da região nordeste do Brasil. Nesta região existem 23 grandes fábricas e aproximadamente 120 minifábricas de beneficiamento de castanha de caju. Essas fábricas geram grande quantidade de cascas que podem ser utilizadas como combustível. Através da conversão térmica da biomassa nos processos de gaseificação e pirólise foi quantificada a produção de resíduo carbonoso, alcatrão, água e gás variando a taxa de aquecimento, a temperatura final e o agente gaseificante (vapor de água, ar sintético ou nitrogênio). Foi verificado que a utilização de vapor de água (1,21 g/min) propicia a geração de um gás de síntese com grande quantidade de hidrogênio (0,99 g) e dióxido de carbono (12,06 g) e para a produção de gás combustível a pirólise com nitrogênio sem a presença de vapor apresenta um gás combustível com poder calorífico mais alto (13056 kJ/m3). / Abstract: Gasification and pyrolysis processes depend on biomass type used providing variations in the distribution of products (tar, ash, water, gas). In the gasification process is achieved mainly a fuel gas which can vary its calorific value according to the temperatures and gasifying agents used. The biomass used in this work is the shell of cashew nuts from the northeast region of Brazil. In this region there are 23 large factories and approximately 120 mini treaters of cashew nuts. These plants generate large quantities of shells that can be used as fuel. Through the thermal conversion processes of biomass gasification and pyrolysis was quantified the production of carbonaceous wastes, tar, water and gas by varying the heating rate, temperature final and gasifying agent (steam, nitrogen or synthetic air). It was found that the use of water vapor (1,21g/min) promotes the generation of a synthesis gas with large quantities of hydrogen (0,99 g) and carbon dioxide (12,06 g) and to produce a pyrolysis fuel gas with nitrogen without the presence of steam shows a fuel gas with heating value higher (13056 kJ/m3). / Doutorado / Termica e Fluidos / Doutor em Engenharia Mecânica

Submitted by Rosangela Silva (rosangela.silva3@unioeste.br) on 2018-06-26T15:19:23Z No. of bitstreams: 2 Rodolfo_Andrade_Schaffner.pdf: 5314013 bytes, checksum: 60ba680e6d87297ff08be073dc0f056c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-06-26T15:19:23Z (GMT). No. of bitstreams: 2 Rodolfo_Andrade_Schaffner.pdf: 5314013 bytes, checksum: 60ba680e6d87297ff08be073dc0f056c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-03-22 / The large production of waste and waste from rural activity must be managed effectively, and cases of treatment by biodigestion are generated more effectively, through the generation of a source of additional income, biogas. Biogas is represented by the mixture rich in CH4 and CO2 and can be used directly by a high temperature or mechanical energy generation, but it is a mixture that can be used as a source of energy of greater value, as synthesis gas. H2 and CO) and in other compounds therefrom, or purified for the choice of hydrogen. In the reform processes it occurs in the presence of catalysts, at high temperatures (600-1200 ºC). For evaluation, many issues that seek more efficient and stable catalysts for these processes, a tertiary operating cities. This work aims to present the results of the study of the conversion of biogas to silica gas using a reforming of the heat measurement system using a high efficiency nickel catalyst supported on Al2O3. Several calcination temperatures of the Al2O3 support (350, 500, 650 and 800 ° C) were studied, as well as the addition of Mg as a promoter (5% by mass). The catalysts were characterized by N2 physiotherapy, X-ray diffraction, desorption at the programmed ammonia temperature and thermogravimetry. The testes were run at 700 ° C, with a spatial distribution of 30 L h-1 gct-1, 1:1 atmosphere and reagent (CH4:CO2). The physical-chemical and activity characteristics of the final Ni/Al2O3 catalysts were studied in the increase of the calcination temperatures generated by the surface areas and pore volume, as well as an increase in the acidity in the lower bands of calcination, and decrease in higher, the greater activity of H2 and CO catalysts. / A grande produção de resíduos e dejetos advindos da atividade rural deve ser gerenciada de forma eficiente sendo que em muitos casos o tratamento por meio de biodigestão anaeróbia é o método mais eficaz, pois gera ao produtor uma possível fonte de renda adicional, o biogás. O biogás é representado pela mistura rica em CH4 e CO2 e pode ser usado diretamente para a geração de energia térmica ou mecânica, porém está mistura pode ser utilizada como insumo para obtenção de outros produtos de maior valor, como gás de síntese (mistura rica em H2 e CO) e em outros compostos a partir deste, ou purificado para obtenção de hidrogênio. Nos processos de reforma a reação ocorre na presença de catalisadores, e em altas temperaturas (600-1200 ºC). Dessa forma, muitos pesquisadores buscam catalisadores mais eficientes e estáveis para estes processos, afim de minimizar as condições operacionais. Este trabalho tem como objetivo apresentar os resultados do estudo da conversão de biogás a gás de síntese, utilizando a reforma a seco (RS) do metano, por meio de reações utilizando catalisadores de níquel de alta eficiência, suportados em Al2O3. Foram estudadas várias temperaturas de calcinação do suporte Al2O3 (350, 500, 650 e 800ºC), além da adição de Mg como promotor (5% em massa). Os catalisadores foram caracterizados por fisissorção de N2, difratometria de raios X, dessorção a temperatura programada de amônia e termogravimetria. Os testes catalíticos foram executados a 700 ºC, com velocidade espacial 30 L h-1 gcat-1, pressão atmosférica e composição da mistura reagente (CH4:CO2) 1:1. Verificou-se que as variáveis estudadas interferem nas características físico-quimicas e de atividade do catalisador final Ni/Al2O3, no qual o aumento das temperaturas de calcinação gerou aumento das áreas superficiais e volume de poros, e também se verificou um aumento da acidez nas faixas mais baixas de calcinação, e redução em temperaturas maiores, o que influenciou na atividade dos catalisadores que mostraram maior atividade em maiores índices de acidez, e em geral melhor formação de H2 e CO.

Submitted by Amanda Silva (amanda.osilva2@ufpe.br) on 2015-03-04T14:11:27Z No. of bitstreams: 2 TESE ALEKSÁNDROS EL ÁURENS MEIRA DE SOUZA.pdf: 8940517 bytes, checksum: 2bc6efe13edc2a11be3c27f8364f8412 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-04T14:11:27Z (GMT). No. of bitstreams: 2 TESE ALEKSÁNDROS EL ÁURENS MEIRA DE SOUZA.pdf: 8940517 bytes, checksum: 2bc6efe13edc2a11be3c27f8364f8412 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2013 / Despontando como nova, mas não necessariamente recente, a tecnologia da miniaturização chega também aos processos químicos. Assim, este trabalho guiou-se com o objetivo de avaliar esta tecnologia no que concerne à concepção e emprego de microssistemas, em especial os microrreatores, desenvolvidos para processos catalíticos, com o intuito de intensificação desses processos, consideradas condições de maior segurança e superação de limites difusionais e térmicos. Foram preparados microrreatores do tipo monólitos em aço Fecralloy®, de 18 mm de diâmetro e 3 cm de comprimento, cada um com canais sinusoidais de 500 μm, tendo sido recobertos por catalisadores específicos para a reforma seca do metano, sendo um de níquel-alumina e outro de níquel/céria-alumina, com massa de fase ativa correspondente a 5,0% em massa (de níquel metálico). Uma vez preparados, os referidos catalisadores foram caracterizados e avaliados quanto ao seu desempenho, em termos de atividade catalítica, frente ao processo químico eleito. A escolha dos catalisadores se deu considerando-se o uso comercial do catalisador de níquel suportado em alumina para as reformas do gás natural, com vistas à obtenção de gás de síntese (syngas) e de hidrogênio, bem como à possibilidade de melhoria de seu desempenho com a dopagem de seu suporte (gama-alumina) com céria (CeO2). Os monólitos recobertos com os catalisadores também foram caracterizados, avaliando-se alguns fatores, dentre os quais sua resistência mecânica, para serem submetidos também a avaliações através da reforma seca do metano e, ao final, serem comparados, em termos de atividade catalítica, conversões, rendimentos e seletividades, com os desempenhos dos catalisadores puros. Os procedimentos de preparação dos catalisadores e monólitos foram realizados em parceria com a Universidad del País Vasco (Espanha), seguindo técnicas já consolidadas pelos seus pesquisadores, e os processos reativos foram levados a efeito no Laboratório de Processos Catalíticos da UFPE. Os procedimentos de formulação e preparação dos catalisadores e monólitos se mostraram eficazes, tendo sido obtidos resultados bastante significativos em termos dos parâmetros avaliados. Conversões de 96% para o metano foram alcançadas com ambos os catalisadores puros. Porém, com os sistemas microestruturados, alcançou-se 97% de conversão para o catalisador de níquel/alumina e próximo dos 100% para o catalisador de níquel/céria-alumina, em tempos espaciais maiores e a temperaturas mais elevadas. Rendimentos e seletividades para o gás de síntese de 88,7% e 94,5%, respectivamente, utilizando-se o catalisador de níquel/céria-alumina, foram verificados com o emprego dos sistemas microestruturados. Razões molares de H2/CO em torno da unidade foram mantidas, como sugerem os processos de reforma seca do metano. Paralelamente, foram realizados estudos termodinâmicos e cinéticos com vistas a uma modelagem do processo avaliado, adotando-se inicialmente parâmetros cinéticos constantes da literatura e ajustando-os ao caso. Balanços mássicos e térmicos foram efetuados, juntamente com considerações difusionais e fluidodinâmicas, para se implementar um modelo usando-se o método dos elementos finitos. Validado o modelo através dos resultados experimentais, foi possível a análise dos fenômenos fluidodinâmicos no interior dos canais dos monólitos concebidos, avaliando-se o comportamento dos componentes reacionais, bem como os perfis de temperatura do sistema.

Face à la demande énergétique de plus en plus croissante, et les problèmes environnementaux qui en découlent, la biomasse, en tant que vecteur énergétique et en association avec des techniques thermochimiques de conversion en gaz combustibles, pourrait être un vecteur énergétique intéressant s’il est produit de manière durable. En effet, accroitre le bouquet énergétique, en substituant d’avantage les énergies fossiles par des énergies renouvelables est devenu une réalité incontournable. De ce fait, les résidus agro-sylvo-pastoraux présentent un potentiel important au Sénégal en général et en particulier dans la région de Ziguinchor jadis appelée grenier du Sénégal, et des technologies de valorisation comme la pyrolyse et gazéification se trouvent parmi les voies les plus prometteuses pour la production d’énergie. Ainsi le modèle dynamique de Saeman basé sur la détermination des propriétés intrinsèques des résidus utilisés a été mis en œuvre afin de simuler l’écoulement de la charge de coques de cajou, de palme et d’arachide. Le modèle dynamique ainsi développé va permettre d'étudier l’influence des conditions opératoires et propriétés rhéologiques sur les profils de chargement, qui conduiront par la suite aux meilleurs transferts de chaleur et de masse dans les fours tournants en situation inerte comme réactive. Les meilleures conditions expérimentales retenues pour cette étude hydrodynamique sont : des vitesses de rotations comprises entre 2 - 4 tr/min, une inclinaison de 1°, et un rapport longueur sur diamètre supérieur ou égal à 0,05. La gazéification des trois résidus sous différents atmosphères (100 % -H2O, 75 % -H2O / 25 %- CO2, 50 % -H2O / 50 % -CO2, 25 % -H2O / 75 % -CO2, et 100 % -CO2) et à différentes températures comprises entre 950 - 1050 °C dans un réacteur à lit fixe ont permis de valider les résultats issus de la littérature qui mettent bien en évidence l’effet positif de la température sur la cinétique de gazéification des différents chars de résidus de biomasse. La pyrolyse de nos trois échantillons donne ainsi des rendements qui sont de 36,44 % pour la coque d’arachide, 37,28 % pour la coque de cajou et 39,97 % pour la coque de palme et quant à leur gazéification, elle conduit respectivement à des énergies d’activation comprises entre 110 - 126 kJ/mol, 104 - 125 kJ/mol et 116 - 150 kJ/mol. Les mesures expérimentales montrent aussi l’influence de la température sur la valeur du PCI des gaz obtenus (8 - 12 MJ/Nm3) et que ce PCI des gaz est inversement proportionnel à la taille des particules de biomasse. Par ailleurs la gazéification sous atmosphère mixte de vapeur d’eau et de gaz carbonique a montré que la réactivité des différents chars est fonction de l’augmentation de la concentration en vapeur d’eau. Le bilan global d’une telle étude expérimentale sur l’hydrodynamique et sur la dégradation thermique visant la maîtrise des phénomènes au sein des fours tournants permet ainsi une première analyse dans la mise en place de combustibles alternatifs pour la valorisation des potentialités locales de la région verte de la Casamance. / In view of the growing energy demand and the resulting environmental problems, biomass as an energy vector and at combination with thermochemical techniques for conversion into combustible gases, could be an interesting energy vector if it is produced in a sustainable manner. Indeed, increasing the energy mix, by replacing fossil fuels with renewable energies, has become an undeniable reality. As a result, agro-sylvo-pastoral residues have significant potential in Senegal in general and in particular in Ziguinchor region, formerly known as Senegal's granary, and valorisation technologies such as pyrolysis and gasification are among the most promising way for energy production. The Seaman’s dynamic model based on the determination of the intrinsic properties of the residues used has been implemented in order to simulate the flow of cashew, palm and peanut shells. Thus, the dynamic model developed will make it possible to study the influence of the operating conditions and rheological properties on the loading profiles which will conduct later of the best heat and mass transfers in the rotating furnaces in inert and reactive conditions. The best experimental conditions for this hydrodynamic study are: rotational speeds between 2 - 4 rpm, inclination of 1 °, and length to diameter ratio greater than or equal to 0.05. The gasification of the three residues under different atmospheres (100 % -H2O, 75 % -H2O / 25 %-CO2, 50 % -H2O / 50 % -CO2, 25 % -H2O / 75 % -CO2, and 100 % -CO2) and at different temperatures between 950 - 1050 °C in a fixed bed reactor enable to validate the results from the literature which clearly show the positive effect of temperature on the gasification kinetics of the various chars. The pyrolysis of our three samples gives yields of 36.44 % for the peanut shell, 37.28 % for the cashew shell and 39.97 % for the palm shell; and when gasified, it leads respectively at activation energies between 110 - 126 kJ / mol, 104 - 125 kJ / mol and 116 - 150 kJ / mol. The experimental measurements also show the influence of temperature on the Lower heating gas values (LHV) obtained (8 - 12 MJ/Nm3) and that, this LHV of gas is inversely proportional to the size of the biomass particles. Moreover, the gasification under mixed atmosphere of steam and carbon dioxide showed that the reactivity of the different chars depend on the increase of the concentration of water vapor. The overall assessment of such an experimental study on the hydrodynamic and thermal degradation of our residues aimed at controlling the phenomena within rotating furnaces (kilns) allows an initial analysis in the setting up of alternative fuels for the valorization of the local potentialities of the green region of Casamance.

Le dioxyde de carbone, principal gaz à effet de serre lié aux activités humaines, est considéré comme l’un des gaz les plus problématiques pour notre environnement ces dernières années, principalement à cause du réchauffement climatique qu’il engendre. C’est pour cette raison que l’augmentation de sa teneur dans l’atmosphère nous concerne tous quant aux conséquences futures pour notre planète. Afin de limiter l’émission de CO2, sa conversion en composés à valeur ajoutée présente un grand intérêt et est possible notamment via des procédés plasmas. Plus particulièrement, les décharges à barrière diélectrique (DBD) sont utilisées depuis quelques années pour générer des plasmas froids opérant à pression atmosphérique, principalement pour des applications en traitement de surface, mais également pour le traitement d’effluents gazeux.Lors de cette thèse, nous nous sommes focalisés sur le processus de dissociation du CO2 en CO et O2 via un réacteur DBD à flux continu et avons analysé sa conversion et son efficacité énergétique via différentes études. Celles-ci ont été réalisées grâce à plusieurs méthodes de diagnostic, comme par exemple la spectrométrie de masse utilisée pour déterminer la conversion et l’efficacité du processus, la spectroscopie d’émission optique, l’oscilloscope pour une caractérisation électrique, etc. afin d’avoir une meilleure compréhension du comportement des décharges CO2.Dans un premier temps, nous avons réalisé une étude détaillée d’un plasma CO2 pur où nous avons fait varier différents paramètres, tels que le temps de résidence, la fréquence, la puissance, la pulsation de la haute tension et l’épaisseur et la nature du diélectrique. Le CO2 donne lieu généralement à une décharge filamentaire, consistant en de nombreuses microdécharges réparties au niveau de la zone du plasma. Celles-ci constituent la principale source de réactivité dans une DBD. Un aperçu détaillé de l’aspect physique de ces microdécharges a été réalisé grâce à la caractérisation électrique, permettant de mieux comprendre les propriétés électriques de la décharge et des microdécharges. En effet, nous avons pu déterminer l’importance de la tension présente au niveau du plasma, de l’intensité du courant plasma, du nombre de microdécharges et de leur temps de vie sur l’efficacité du processus de dissociation de CO2.Ensuite, nous avons conclu ce travail avec des études combinant le CO2 en phase plasma avec de l’eau ou du méthane afin de produire des molécules à valeur ajoutée telles que les syngas (CO et H2), mais aussi des hydrocarbures (C2H6, C2H4, C2H2 et CH2O) dans le cas de l’ajout du méthane. A travers ces études, nous avons obtenu une meilleure connaissance de la chimie et de la physique qui ont lieu dans ce type de plasma. / Carbon dioxide appears as one of the most problematic gases for the environment, mostly because it is responsible for global warming. This is why its increasing concentration into the atmosphere, mainly due to anthropogenic activities, is a real concern for planet Earth. In order to prevent the release of large amounts of CO2, its conversion into value-added products is of great interest. In this context, plasma-based treatments using dielectric barrier discharges (DBDs) are nowadays more and more used for the conversion of this gas. In this thesis, we investigated the CO2 splitting process into CO and O2 via a flowing cylindrical DBD and we studied its conversion and energy efficiency by means of several diagnostic methods, such as mass spectrometry to determine the conversion and energy efficiency of the process, optical emission spectroscopy for gas temperature measurements, and an oscilloscope for electrical characterization, in order to obtain a better understanding of the CO2 discharge itself.First, we focused on an extensive experimental study of a pure CO2 plasma where different parameters were varied, such as the gas residence time, the operating frequency, the applied power, the pulsation of the AC signal, the thickness and the nature of the dielectric. CO2 discharges typically exhibit a filamentary behavior, consisting of many microdischarges, which act as the main source of reactivity in a DBD. A detailed insight in the physical aspects was achieved by means of an in-depth electrical characterization, allowing more insight in the electrical properties of the discharge and more specifically in the microdischarges, which are spread out throughout the active zone of the plasma. It was found throughout this work that the plasma voltage, which reflects the electric field and thus determines how the charged particles are accelerated, the plasma current, which reflects the electron density, but also the number of microdischarges and their average lifetime, play an important role in the efficiency of the CO2 dissociation process. It was revealed that the microdischarge number is important as it represents the repartition of the locations of reactivity. Indeed, as the microfilaments are more spread out in the same discharge volume, the probability for the CO2 molecules to pass through the reactor and interact with at least one microdischarge filament becomes more important at a larger number of microfilaments.The second part of the thesis was dedicated to discharges combining CO2 and H2O or CH4, both being hydrogen source molecules. The combined CO2/H2O or CO2/CH4 conversion allows forming value-added products like syngas (CO and H2), but also hydrocarbons (C2H6, C2H4, C2H2 and CH2O), at least in the presence of methane. Throughout this study, we tried to obtain a better knowledge of the chemistry and physic behind these conversion processes. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

In the effort to introduce fuel cell technology in the field of decentralized and mobile power generators, a hydrocarbon reformer to syngas seems to be the way for the market uptake. In this thesis, a potential technology is developed and investigated, in order to convert commercial liquid fuel (diesel, kerosene and biodiesel) to syngas. The fundamental concept is to oxidise the fuel in a oxygen depleted environment, obtaining hydrogen and carbon monoxide as main products of the reaction. In order to extend the flammability limit of hydrocarbon/air mixtures, the rich combustion experiments have been carried out in a two-layer porous medium combustor, which stabilises a flame at the matrix interface and recirculates the enthalpy of the hot products in order to enhance the reaction rates at ultra-rich equivalence ratio. This thesis demonstrates the feasibility of the concept, by exploring characteristic parameters for a compact, reliable and cost effective device. Specifically, a range of equivalence ratios, thermal loads and porous materials have been examined. n-heptane was successfully reformed up to an equivalence ratio of 3, reaching a conversion efficiency (based on the lower heating value of H2 and CO over the fuel input) up to 75% for a packed bed of alumina beads. Thermal loads from P=2 to 12 kW at phi=2.0 demonstrated that heat losses can be reduced to 10%.Similarly, diesel, kerosene and bio-diesel were reformed to syngas in a Zirconia foam burner with conversion efficiency over 60%. The effect of different burners, thermal loads and equivalence ratios have also been assessed for these commercial fuels, leading to equivalent conclusions. A preliminary attempt to reduce the content of CO and hydrocarbons in the reformate has been also performed using commercial steam reforming and water-gas shift reaction catalysts, obtaining encouraging results. Finally, soot emission has been assessed, demonstrating particle formation for all the fuels above phi=2.0, with biodiesel showingthe lowest soot formation tendency among all the fuels tested.