Influência do tipo de distribuidor na fluidodinâmica de uma mistura biomassa-areia em leito fluidizado
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Data
2019-08-01
Autores
Balestieri, Fernando Manente Perrella
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O leito fluidizado é um sistema que é utilizado na indústria para diversos tipos de aplicações, variando desde craqueamento de petróleo e processamento de materiais como silício e urânio até secagem de grãos. Dentre esses diversos processos, o leito fluidizado também pode ser aplicado em processos termoquímicos como combustão e gaseificação de biomassa, apresentando vantagens como alta eficiência, perfil térmico homogêneo, além de flexibilidade de combustível. No entanto, o uso da biomassa no leito ainda gera algumas dificuldades, principalmente para partículas como a casca de arroz, que não fluidizam tão facilmente. Para contornar esse problema, normalmente é acrescentado um material inerte e barato como a areia. Essa mistura binária de biomassa e inerte pode gerar outros problemas, como segregação do material particulado, caminhos preferenciais do gás e pontos de estagnação, o que reduz consideravelmente a eficiência do sistema. Portanto, passa a ser importante entender como os diferentes parâmetros existentes no leito influenciam no comportamento dessa mistura para conseguir evitar esses problemas. Nesse trabalho foi feito uma análise comparativa avaliando 3 fatores: tipo de placa distribuidora (perfurada e com injetores tuyere), responsável por injetar o gás de fluidização no leito, a granulometria do material inerte (675 e 325 μm) e porcentagem de casca de arroz (1% até 10% da massa total). Esses fatores foram alterados separadamente para explorar a influência que eles causam no nível de mistura do leito entre os dois particulados (índice de mistura) assim como na velocidade de mínima fluidização e na expansão do leito. Também foram feitos experimentos para obter o comportamento térmico do material particulado para a combustão e gaseificação, relacionando esses dados com os obtidos no leito. Os resultados indicam que a placa com injetores gera uma maior queda de pressão, mas diminui os pontos de estagnação e melhora o nível de mistura do leito se comparado com a placa perfurada. O aumento da granulometria e da proporção de casca de arroz pioram a fluidização, geram canais preferenciais e aumentam a velocidade de mínima fluidização. A expansão do leito parece ser mais influenciada pela proporção de casca. O comportamento térmico da casca de arroz e da mistura casca/areia tiveram comportamentos diferentes, indicando que areia tem a função de não apenas auxiliar na fluidização, mas de reduzir a temperatura de funcionamento do leito em um processo de gaseificação.
The fluidized bed is a system used in the industry for a variety of applications, ranging from oil cracking and processing of materials such as silicon and uranium to grain drying. Among these several processes, the fluidized bed can also be applied in thermochemical processes such as biomass combustion and gasification, presenting advantages such as high efficiency, homogeneous thermal profile, and fuel flexibility. However, the use of the biomass in the bed still generates some difficulties, especially for particles like the rice husk, that do not fluidize so easily. To work around this problem, an inert, inexpensive material such as sand is usually added to the bed. This binary mixture of biomass and inert can create other problems, such as segregation of the particulate solids, gas preference paths and stagnation points, which considerably reduces the efficiency of the system. Thus, it becomes important to understand how these different parameters in the bed influence the behavior of the mixture to avoid these problems. In this work a comparative analysis was carried out evaluating 3 factors: type of distribution plate (perforated and with tuyere injectors), responsible for injecting the fluidization gas in the bed, the inert granulometry (675 and 325 μm) and percentage of rice husk (1% to 10% of the total mass). These factors were altered separately to explore the influence they cause on the level of bed mixing between the two particulates (mixing index) as well as the velocity of minimum fluidization and bed expansion. Experiments were also conducted to obtain the thermal behavior of the particulate for combustion and gasification, relating these data to those obtained in the bed. The results indicate that the tuyere injectors plate generates a greater pressure drop, but decreases the stagnation points and improves the bed mixing level when compared to the perforated plate. The increase in grain size and the proportion of rice husks worsen fluidization, generate preferential channels and increase the minimum fluidization velocity. The bed expansion seems to be more influenced by the proportion of rice husk. The thermal behavior of the rice husk and the rice husk/sand mixture had different behaviors, indicating that sand has the function of not only assisting in fluidization but also of reducing the bed operating temperature in a gasification process
The fluidized bed is a system used in the industry for a variety of applications, ranging from oil cracking and processing of materials such as silicon and uranium to grain drying. Among these several processes, the fluidized bed can also be applied in thermochemical processes such as biomass combustion and gasification, presenting advantages such as high efficiency, homogeneous thermal profile, and fuel flexibility. However, the use of the biomass in the bed still generates some difficulties, especially for particles like the rice husk, that do not fluidize so easily. To work around this problem, an inert, inexpensive material such as sand is usually added to the bed. This binary mixture of biomass and inert can create other problems, such as segregation of the particulate solids, gas preference paths and stagnation points, which considerably reduces the efficiency of the system. Thus, it becomes important to understand how these different parameters in the bed influence the behavior of the mixture to avoid these problems. In this work a comparative analysis was carried out evaluating 3 factors: type of distribution plate (perforated and with tuyere injectors), responsible for injecting the fluidization gas in the bed, the inert granulometry (675 and 325 μm) and percentage of rice husk (1% to 10% of the total mass). These factors were altered separately to explore the influence they cause on the level of bed mixing between the two particulates (mixing index) as well as the velocity of minimum fluidization and bed expansion. Experiments were also conducted to obtain the thermal behavior of the particulate for combustion and gasification, relating these data to those obtained in the bed. The results indicate that the tuyere injectors plate generates a greater pressure drop, but decreases the stagnation points and improves the bed mixing level when compared to the perforated plate. The increase in grain size and the proportion of rice husks worsen fluidization, generate preferential channels and increase the minimum fluidization velocity. The bed expansion seems to be more influenced by the proportion of rice husk. The thermal behavior of the rice husk and the rice husk/sand mixture had different behaviors, indicating that sand has the function of not only assisting in fluidization but also of reducing the bed operating temperature in a gasification process
Descrição
Palavras-chave
Leito fluidizado borbulhante., Biomassa., Casca de arroz., Distribuidor., Índice de mistura., Bubbling fluidized bed, Biomass, Rice husk, Mixing index, Leito fluidizado (Pirometalurgia), Materiais granulados