Estudo termogravimétrico da absorção de dióxido de enxofre por calcário
Data
2017-11-15
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Biblioteca Digital de Teses e Dissertações da USP
Universidade de São Paulo
Escola de Engenharia de São Carlos
Universidade de São Paulo
Escola de Engenharia de São Carlos
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Neste trabalho determina-se, através da termogravimetria, o efeito da temperatura e atmosfera sobre a conversão, a cinética e a efetividade da absorção de 'SO IND.2' por calcário. Aplica-se temperaturas e tamanho de particulado típicos do processo de combustão de carvão em leito fluidizado. Foram realizados ensaios isotérmicos em diferentes temperaturas (entre 650 e 950 graus Celsius), na pressão atmosférica local (~ 697 mmHg), em atmosferas dinâmicas de ar e de nitrogênio. Os resultados de sulfatação foram avaliados empregando-se a cinética de Arrhenius. A ordem de grandeza dos valores de energia de ativação obtidos (4,446 kJ/mol em ar e 3,748 kJ/mol em nitrogênio) sugere que o processo reativo seja controlado por difusão de Knudsen. A temperatura ótima de conversão resultou entre 800 e 850 graus Celsius em ar, e muito próxima de 900 graus Celsius em nitrogênio. Definiu-se efetividade como a relação entre o coeficiente de taxa de reação instantâneo e o seu valor máximo, indicando o decaimento temporal da reatividade da amostra com o progresso da sulfatação. Determinou-se a efetividade média para todas as temperaturas no intervalo de tempo em que a sulfatação se desenvolveu, sempre em torno de 200 s nos vários ensaios. Os maiores valores de efetividade média foram a 800 graus Celsius em atmosfera de ar (0,2854), e a 900 graus Celsius em atmosfera de nitrogênio (0,3142)
In this work thermogravimetry is applied to determine the effect of temperature and atmosphere on conversion, kinetics and effectiveness of 'SO IND.2' absorption by limestone. Ranges of temperature and particle size were applied that are typical of the fluidized bed coal combustion process. Isothermal experiments were performed for different temperatures (between 650 and 950 Celius degrees), at local atmospheric pressure (~ 697 mmHg), in dynamic atmospheres of air and nitrogen. The results of sulfation were evaluated using Arrhenius' kinetics. The order of magnitude of the resulting activation energies (4.446 kJ/mol in air and 3.748 kJ/mol in nitrogen) suggest the reaction to be controlled by Knudsen diffusion. Optimum conversion resulted between 800 and 850 Celsius degrees in ar, and around 900 Celsius degrees in nitrogen. Effectiveness was defined as the ratio between the instantaneous reaction rate coefficient and its maximum value, indicating the time decay of reactivity as sulfation advances. The average effectiveness was determined for all the temperatures considering the whole sulfation time interval, which was always around 200 seconds. The highest values of average effectiveness were found at 800 Celsius degrees in air atmosphere (0,2854), and 900 Celsius degrees in nitrogen atmosphere (0,3142)
In this work thermogravimetry is applied to determine the effect of temperature and atmosphere on conversion, kinetics and effectiveness of 'SO IND.2' absorption by limestone. Ranges of temperature and particle size were applied that are typical of the fluidized bed coal combustion process. Isothermal experiments were performed for different temperatures (between 650 and 950 Celius degrees), at local atmospheric pressure (~ 697 mmHg), in dynamic atmospheres of air and nitrogen. The results of sulfation were evaluated using Arrhenius' kinetics. The order of magnitude of the resulting activation energies (4.446 kJ/mol in air and 3.748 kJ/mol in nitrogen) suggest the reaction to be controlled by Knudsen diffusion. Optimum conversion resulted between 800 and 850 Celsius degrees in ar, and around 900 Celsius degrees in nitrogen. Effectiveness was defined as the ratio between the instantaneous reaction rate coefficient and its maximum value, indicating the time decay of reactivity as sulfation advances. The average effectiveness was determined for all the temperatures considering the whole sulfation time interval, which was always around 200 seconds. The highest values of average effectiveness were found at 800 Celsius degrees in air atmosphere (0,2854), and 900 Celsius degrees in nitrogen atmosphere (0,3142)
Palavras-chave
calcário, termogravimetria, sulfatação, dióxido de enxofre, cinética química, limestone, sulfation, sulfur dioxide, chemical kinetics, thermogravimetry