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Previous issue date: 2016-01-29 / Tecnologias existentes para a captura e sequestro de CO2 tornam o processo muitas vezes invi?vel industrialmente, pois exige um alto consumo de energia, levando a uma redu??o na efici?ncia da planta e aumentando o custo de produ??o. Por isso, a fim de amenizar a emiss?o de gases de efeito estufa, tem-se focado na utiliza??o de energias alternativas e no aumento da efici?ncia na convers?o e utiliza??o de energia. Recircula??o Qu?mica para Combust?o (RQC) e reforma (RQR) est?o entre as melhores alternativas para reduzir a emiss?o de CO2, pois facilitam sua captura com baixo custo e sem perda de efici?ncia energ?tica substancial. O sistema reacional baseia-se na transfer?ncia de oxig?nio do ar para um combust?vel, atrav?s de um transportador s?lido de oxig?nio (TSO) que circula entre dois reatores de leito fluidizado. As rea??es de combust?o ocorrem na superf?cie dos TSO, sendo este, quest?o chave para o desenvolvimento e dimensionamento da tecnologia de RQC. Tendo em vista que ainda h? a necessidade de se estudar o comportamento dos TSOs a fim de obter um transportador adequado para a tecnologia de recircula??o qu?mica, o presente trabalho teve como objetivo realizar um estudo dos TSOs para RQC e RQR, utilizando hidrog?nio, metano e etanol como combust?vel. Dois TSOs, ? base de Ni e Cu, foram avaliados quanto as suas reatividades, bem como o estudo termodin?mico foi realizado para esse processo. Para esse estudo, uma caracteriza??o do TSO ? base de Cu, foi realizada utilizando diferentes concentra??es m?ssicas de Cu. Os resultados mostraram que o aumento da concentra??o de cobre a ser adicionado no suporte diminuiu o tamanho dos poros provocado por uma aglomera??o do metal ativo, restando apenas um percentual na superf?cie. Mudan?as significativas na temperatura de redu??o n?o foram observadas com o a aumento da concentra??o de Cu. Em geral, todos os TSO ? base de Cu atingiram convers?o m?xima, utilizando etanol como combust?vel, mostrando ser bastante reativos. Verificou-se ainda que quanto maior o teor de ?xido met?lico, menor ? a velocidade de rea??o. Para as baixas concentra??es de adi??o de cobre, o modelo de nuclea??o apresentou melhor descri??o dos dados experimentais. J? para as maiores concentra??es de adi??o de cobre e com adi??o de 1% de c?rio, o modelo shrinking core correlacionou melhor os dados experimentais. Com rela??o ao sistema redox CuO/Cu, observou-se que valores altos da constante de equil?brio (Keq) foram obtidos para as temperaturas investigadas, mostrando que a convers?o praticamente completa dos combust?veis ? obtida. O aumento da temperatura provocou uma diminui??o da Keq, por?m altas temperaturas foram necess?rias para a completa redu??o do TSO. A varia??o da energia de Gibbs foi m?nima para as temperaturas relevantes para RQC, indicando que a rea??o de combust?o ocorre de maneira espont?nea. Para o TSO ? base de Ni, amostras comerciais foram utilizadas. Este mostrou ser bem reativo, apresentando convers?es superiores a 90% utilizando como combust?veis H2 e CH4 e CH4 + H2O. Temperaturas altas, em torno de 900 ?C foram necess?rias para uma alta convers?o. O modelo shrinking core obteve uma boa descri??o dos dados experimentais, apresentando baixo erro para convers?es menores que 0,8, enquanto que o modelo de difus?o descreveu melhor os dados experimentais com convers?es superiores a 0,8. / Existing technologies for CO2 capture and sequestration oftentimes make the process industrially infeasible because it demands a high power consumption, leading to a reduction in plant efficiency and increasing the cost of production. Therefore, in order to mitigate the emission of greenhouse gases, has focused on the use of alternative energy and increased efficiency in conversion and use of energy. Chemical Looping Combustion (CLC) and Reform (CLR) are among the best alternatives to reduce CO2 emissions, because they facilitate his capture with low cost and without substantial loss of energy efficiency. The reaction system is based on oxygen transfer on the air into a fuel through a solid oxygen carrier (SOC) which circulates between two fluidized bed reactors. Combustion reactions occur on the surface of the SOC, which is, key issue for the development and sizing from CLC technology. In view of that there is still the necessity of study the behavior of SOCs in order to obtain a suitable carrier for the chemical looping technology, this work had as objective carry out a study of the SOCs for CLC and CLR using hydrogen, methane and ethanol as fuels. Two SOCs, to the based on Ni and Cu, were assessed according their reactivities, as well as the thermodynamic study was performed for this process. For this study, an characterization of SOC to Cu base was perfomed different mass concentrations of Cu. The results showed that the concentration of copper to be added to the support decreased size pore inflict on by sintering of the active metal, leaving only a percentage at the surface. Significant changes in the reduction temperature were not observed with the increase in Cu concentration. In general, all the SOC to Cu base reached maximum conversion using ethanol as fuel, showing to be quite reactive. It was also found that the higher the metal oxide content, the lower the reaction rate. For the addition of low concentrations of copper, the nucleation model showed better description of the experimental data. Already for the higher concentrations of copper addition and with addition of 1% cerium, the shrinking core model correlated better to experimental data. Regarding the redox system CuO / Cu, it was observed that high values of equilibrium constant (Keq) were obtained for the temperatures investigated, showing virtually complete conversion of the fuel is obtained. Increasing the temperature resulted in a decrease of Keq, but higher temperatures are required for complete reduction of the SOC. The variation of Gibbs energy was minimal for the relevant temperatures for CLC, indicating that the combustion reaction occurs spontaneously. For Ni-based SOC, commercial samples were used. This proved to be very reactive, with conversions greater than 90% using CH4 and H2 and CH4 + H2O as fuels. High temperatures, around 900 ?C were required for a high conversion. The shrinking core model obtained a good description of the experimental data presenting low error for lower conversions than 0.8, while the diffusion model described better the experimental data with conversions greater than 0.8.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/24983 |
| Date | 29 January 2016 |
| Creators | Figueredo, Adolfo Lopes de |
| Contributors | 27111541812, Oliveira, Humberto Neves Maia de, 22179763468, Ruiz, Juan Alberto Chavez, 00744293456, Chiavone Filho, Osvaldo, Pereira, Camila Gambini |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM ENGENHARIA QU?MICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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