Carregar apresentação
A apresentação está carregando. Por favor, espere
1
SECAGEM DE GRÃOS EM ALTAS TEMPERATURAS
Prof. Daniel Marçal de Queiroz Viçosa, MG Agosto/2002 _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
2
Classificação dos secadores quanto ao fluxo de produto
leito fixo fluxos cruzados fluxos concorrentes fluxos contracorrentes fluxos mistos estacionários contínuos intermitentes _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
3
Secador de leito fixo ou de camada estacionária
Constituição: sistema de aquecimento de ar ventilador câmara de distribuição de ar ou plenum câmara de secagem Características: configuração simples baixo custo _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
4
Secador de Camada Fixa Modelo UFV
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Modelo UFV
5
Secador de leito fixo ou de camada estacionária
Manejo do secador de leito fixo variáveis de projeto do secador: potência do sistema de movimentação de ar área da câmara de secagem altura máxima da camada variáveis relacionadas com o produto e o ambiente: tipo de produto altitude do local temperatura e umidade relativa ambiente temperatura e umidade inicial do produto _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
6
Secador de leito fixo ou de camada estacionária
Manejo do secador de leito fixo variáveis de controle: espessura da camada de grãos temperatura de secagem revolvimento do produto repouso do produto resultado: resistência ao fluxo de ar gradiente de umidade na camada de grãos consumo de energia qualidade do produto final _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
7
Secador de leito fixo ou de camada estacionária - Top Dry
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Secagem em leito fixo no topo do silo, resfriamento na parte inferior.
8
Secador de leito fixo ou de camada estacionária - com sistema de revolvimento
Componentes: Silo metálico Piso plano perfurado Ventilador Aquecedor Revolvedor de grãos Espalhador Sistema de descarga
9
Secador de leito fixo ou de camada estacionária - com sistema de revolvimento
Secagem em silos com revolvimento da massa de grãos: alturas de camada de até 5,50 m, temperaturas de secagem de até 60o C. Fluxo de ar aumenta em até 33% com o uso do revolvedor. _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
10
Secador de leito fixo ou de camada
estacionária - com sistema de revolvimento Detalhe do sistema de revolvimento
11
Secador de leito fixo ou de camada estacionária
Sistema utilizado no Brasil para secagem de amendoim. _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
12
Secador de leito fixo ou de camada estacionária
Problema: gradiente de umidade na camada, para contornar o problema utilizar temperaturas de secagem entre 35 a 40o C. _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
13
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Convecção Natural
14
Secadores em cascata ou de calhas
Câmaras de secagem e resfriamento constituídas por uma série de calhas invertidas Fileiras de calhas espaçadas de 20 a 30 cm Grãos movimentam-se por gravidade Ar de secagem ou resfriamento entra por uma linha de calhas e sai pelas linhas imediatamente superior e inferior Ora o fluxo de ar é concorrente ora é contracorrente ao fluxo de produto Primeiros secadores eram dotados de ventiladores centrífugos, hoje quase todos os fabricantes utilizam ventiladores axiais _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
15
Secadores em cascata ou de calhas
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
16
Secadores em cascata ou de calhas
Produto a ser seco deve apresentar baixo teor de impurezas caso contrário o fluxo de produto pode tornar-se desuniforme Existe um limite abaixo do qual o fluxo de produto não pode ser reduzido À medida em que se reduz a velocidade do produto dentro do secador pode ocorrer desuniformidade do fluxo de produto Secador pode ser operado em regime contínuo apenas quando a umidade inicial é igual ou inferior a 18% Para melhorar a eficiência energética os secadores passar a serem fabricados com opção de reaproveitamento do ar de resfriamento e de exaustão _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
17
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Secadores de Calhas
18
com reproveitamento do ar de resfriamento e sistema de coleta de
Secador tipo cascata com reproveitamento do ar de resfriamento e sistema de coleta de partículas _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
19
Secadores em cascata ou de calhas
Temperaturas de secagem Milho e soja para consumo: 100o C Trigo para consumo: 70o a 80o C Arroz: 70o a 80o C Sementes: 50o a 60o C (não permitir os grãos atinjam temperaturas superiores a 43o C _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
20
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
21
Secadores de fluxos cruzados
Secador mais usado no mundo Configuração, construção e operação simples Passagem do ar perpendicular à passagem dos grãos que se movem entre duas chapas perfuradas Espessura da camada de grãos: 20 a 30 cm _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
22
Secadores de fluxos cruzados
Secador convencional: problemas com gradiente de umidade e elevado consumo de energia Para melhorar desempenho: reversão do fluxo de ar e reversão da camada de grãos para reduzir o gradiente de umidade na camada reaproveitamento do ar de exaustão para reduzir o consumo de energia _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
23
Secador de fluxos cruzados
Esquema básico _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
24
Secadores de fluxos cruzados
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
25
Secadores de fluxos cruzados
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Secador é modular permitindo diferentes configurações para obtenção de diferentes capacidades de secagem.
26
Secadores de fluxos cruzados
Eclusas próximas à entrada de ar descarregam o produto mais rápido para reduzir o gradiente de umidade na camada. _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
27
Recirculação do ar _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
29
Secadores de fluxos concorrentes
Ar e grãos fluem no mesmo sentido Altas taxas de evaporação ocorrem na parte superior da camada, uma vez que o ar mais quente encontra o grão mais úmido Trocas intensas de energia e massa ocorrem quando o ar encontra o produto Temperatura do produto permanece consideravelmente abaixo da temperatura do ar de secagem Resfriamento é geralmente feito em fluxos contracorrentes _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
30
Secadores de fluxos concorrentes
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
31
Secadores de fluxos concorrentes
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
32
Secadores de fluxos concorrentes
Vantagens: Melhor qualidade final do produto Maior capacidade de secagem. Alta eficiência energética. Baixo custo de instalação e manutenção _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
33
Secadores de fluxos contracorrentes
O ar de secagem e grãos fluem em sentido contrário. A frente de secagem permanece sempre próxima ao fundo perfurado. À medida que o produto desce, sua temperatura aumenta, ficando próximas à temperatura do ar de secagem. A temperatura de secagem não deve ultrapassar 70oC. _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
34
Secadores intermitentes
Produto ao passar pelo secador retorna à parte superior do secador Quando dotados de câmaras de repouso geralmente o produto permanece 10% na câmara de secagem e o restante do tempo na câmara repouso Câmaras de repouso: melhor eficiência energética e melhor qualidade do produto final _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
35
Secadores intermitentes
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
36
Secagem em combinação Secagem em altas temperaturas até o produto atingir 16% a 18% de umidade Secagem em baixas temperaturas no final do processo de secagem Melhor eficiência energética e melhor qualidade do produto final _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
37
Seca-aeração _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
38
Aumento da capacidade de secagem do secador: 50% a 75%
Seca-Aeração Aumento da capacidade de secagem do secador: 50% a 75% Redução do consumo de energia: 20% a 40% Melhoria da qualidade do produto final ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Apresentações semelhantes
