Avaliação da eficiência de secagem de café (Coffea arabica L.), em secador de camada fixa vertical com revolvimento mecânico
Arquivos
Data
1999
Autores
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Universidade Federal de Viçosa
Resumo
Com o objetivo de avaliar a eficiência de secagem e a redução das diferenças de teor de umidade e temperatura entre os pontos de entrada e saída do ar na câmara de secagem, em um secador de camada fixa com sistema de revolvimento mecânico, foram conduzidos cinco testes de secagem, utilizando cinco diferentes intervalos de revolvimento do produto (2, 3, 4, 5 e 6 h). A temperatura do ar de secagem na massa de café foi controlada de forma a não ultrapassar 40 o C, com fluxo de ar de 11,7 m 3 .min -1 .m -2 . Os teores de umidade iniciais do produto foram diferentes em cada teste realizado. Com o intuito de avaliar a uniformidade da massa de grãos quanto ao teor de umidade, foram realizadas amostragens do produto em dois pontos de cada câmara de secagem, antes e depois de cada revolvimento realizado. Para avaliar a uniformidade de temperatura do ar de secagem na massa de grãos e no plenum foram instalados termopares ligados a um sistema de aquisição de dados, os quais registravam as temperaturas em intervalos de 10 min. Com os resultados obtidos verificou-se que as câmaras de secagem 1 e 4 apresentam maior temperatura do ar de secagem na massa de grãos, evidenciando uma possível má distribuição do fluxo de ar no plenum do secador. A maior diferença de teor de umidade no sentido horizontal da câmara de secagem observada antes do revolvimento, foi para o teste com intervalo de revolvimento de 5 h. A maior diferença de temperatura no sentido horizontal da
câmara de secagem observada antes do revolvimento foi no teste com intervalo de revolvimento de 4 h. As menores diferenças tanto de teor de umidade quanto de temperatura no sentido horizontal da câmara de secagem, antes do revolvimento foram observadas no teste com intervalo de revolvimento de 2 h. A operação de revolvimento mostrou-se eficaz na diminuição das diferenças tanto de teor de umidade quanto de temperatura. O secador apresentou alto consumo específico de energia e baixa eficiência de secagem, devido, possivelmente, aos fatos de que a fornalha de aquecimento direto a carvão vegetal não estava adequadamente dimensionada para o secador utilizado, e que o fluxo de ar de secagem estava muito alto para a espessura de camada utilizada. O combustível utilizado para aquecimento do ar de secagem e demais procedimentos utilizados nos testes não influenciaram a qualidade do produto no que diz respeito ao "tipo" e "bebida".
Five drying tests were carried out using five different intervals for coffee revolving (2, 3, 4, 5 and 6) in order to evaluate the drying efficiency and the reduction of the differences in moisture content and temperature between the air entry and exit points at the drying chamber in a fixed layer dryer with mechanical revolving. The drying air temperature on coffee mass was controlled in such a way not exceeding 40 o C with an air flow of 11.7 m 3 .min -1 .m -2 . The initial moisture contents were different at each test. To evaluate the uniformity of the grain mass for moisture content the coffee samplings were performed at two points in the dryer chamber before and after each mechanical revolving. To evaluate the uniformity of the drying air temperature on the grain mass and plenum, the installation of thermocouples were performed by connecting them to a data acquisition system which registered the temperatures at 10 min intervals. According to the obtained results, the following were verified: the drying chambers 1 and 4 presented a higher drying air temperature on the grain mass, so evidencing a possibility for unsatisfactory distribution of the air flow at the dryer plenum. The greatest difference for moisture content on the horizontal direction of the drying chamber was observed before grain revolving for the test with 5 h - revolving interval. The greatest difference for temperature on the horizontal direction of the drying chamber was observed before grain revolving for the test with the 4 h - revolving interval. The lowest differences for either moisture content and temperature on the horizontal direction of the drying chamber was observed before grain revolving for the test with 2 h - revolving interval. The grain revolving operation showed to be efficient in diminishing the differences for either moisture content and temperature. The dryer presented high specific energy consumption as well as low drying efficiency probably because the directly heating charcoal furnace was not adequately dimensioned to the used dryer and also the drying air flow was very high for the thickness of the used layer. The fuel used for heating the drying air and the other procedures used in the tests did not influence the product quality relatively to their "type" and "drinking".
Five drying tests were carried out using five different intervals for coffee revolving (2, 3, 4, 5 and 6) in order to evaluate the drying efficiency and the reduction of the differences in moisture content and temperature between the air entry and exit points at the drying chamber in a fixed layer dryer with mechanical revolving. The drying air temperature on coffee mass was controlled in such a way not exceeding 40 o C with an air flow of 11.7 m 3 .min -1 .m -2 . The initial moisture contents were different at each test. To evaluate the uniformity of the grain mass for moisture content the coffee samplings were performed at two points in the dryer chamber before and after each mechanical revolving. To evaluate the uniformity of the drying air temperature on the grain mass and plenum, the installation of thermocouples were performed by connecting them to a data acquisition system which registered the temperatures at 10 min intervals. According to the obtained results, the following were verified: the drying chambers 1 and 4 presented a higher drying air temperature on the grain mass, so evidencing a possibility for unsatisfactory distribution of the air flow at the dryer plenum. The greatest difference for moisture content on the horizontal direction of the drying chamber was observed before grain revolving for the test with 5 h - revolving interval. The greatest difference for temperature on the horizontal direction of the drying chamber was observed before grain revolving for the test with the 4 h - revolving interval. The lowest differences for either moisture content and temperature on the horizontal direction of the drying chamber was observed before grain revolving for the test with 2 h - revolving interval. The grain revolving operation showed to be efficient in diminishing the differences for either moisture content and temperature. The dryer presented high specific energy consumption as well as low drying efficiency probably because the directly heating charcoal furnace was not adequately dimensioned to the used dryer and also the drying air flow was very high for the thickness of the used layer. The fuel used for heating the drying air and the other procedures used in the tests did not influence the product quality relatively to their "type" and "drinking".
Descrição
Dissertação de Mestrado defendida na Universidade Federal de Viçosa
Palavras-chave
Café Secagem Eficiência Secador de camada fixa Revolvimento mecânico Gradiente de teor de umidade Gradiente de temperatura, Coffee Drying efficiency Fixed-bed dryer Mechanical revolving system Moisture content differences
Citação
De Grandi, Adriana Maria. Avaliação da eficiência de secagem de café (Coffea arabica L.), em secador de camada fixa vertical com revolvimento mecânico. Viçosa : UFV, 1999. 61p. (Dissertação - mestrado em Engenharia Agrícola) Orientador: Evandro de Castro Melo. T 633.7368 D321a 1999