Secagem Graos Altas Temperaturas (1)
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Transcript of Secagem Graos Altas Temperaturas (1)
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SECAGEM DE GROS EM ALTAS TEMPERATURASProf. Daniel Maral de Queiroz
Viosa, MGAgosto/2002
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Classificao dos secadores quanto ao fluxo de produtoleito fixofluxos cruzadosfluxos concorrentesfluxos contracorrentesfluxos mistos
estacionrioscontnuosintermitentes
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Secador de leito fixo ou de camada estacionriaConstituio:sistema de aquecimento de arventiladorcmara de distribuio de ar ou plenumcmara de secagem
Caractersticas:configurao simplesbaixo custo
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Secador de Camada FixaModelo UFV
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Secador de leito fixo ou de camada estacionriaManejo do secador de leito fixovariveis de projeto do secador:potncia do sistema de movimentao de arrea da cmara de secagem altura mxima da camada
variveis relacionadas com o produto e o ambiente:tipo de produtoaltitude do localtemperatura e umidade relativa ambientetemperatura e umidade inicial do produto
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Secador de leito fixo ou de camada estacionriaManejo do secador de leito fixovariveis de controle:espessura da camada de gros temperatura de secagemrevolvimento do produtorepouso do produto
resultado:resistncia ao fluxo de argradiente de umidade na camada de grosconsumo de energiaqualidade do produto final
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Secador de leito fixo ou de camada estacionria - Top Dry
Secagem em leito fixo no topo do silo, resfriamento na parte inferior.
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Secador de leito fixo ou de camada estacionria - com sistema de revolvimentoComponentes:Silo metlicoPiso plano perfuradoVentiladorAquecedorRevolvedor de grosEspalhadorSistema de descarga
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Secador de leito fixo ou de camada estacionria - com sistema de revolvimento
Secagem em silos com revolvimento da massa de gros: alturas de camada de at 5,50 m, temperaturas de secagem de at 60o C. Fluxo de araumenta em at 33%com o uso do revolvedor.
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Secador de leito fixo ou de camada estacionria - com sistema de revolvimentoDetalhe dosistema derevolvimento
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Secador de leito fixo ou de camada estacionria
Sistema utilizado no Brasil para secagem de amendoim.
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Secador de leito fixo ou de camada estacionria
Problema: gradiente de umidadena camada, para contornar o problema utilizar temperaturas de secagem entre 35 a 40o C.
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Conveco Natural
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Secadores em cascata ou de calhasCmaras de secagem e resfriamento constitudas por uma srie de calhas invertidas
Fileiras de calhas espaadas de 20 a 30 cm
Gros 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 concorrente ora contracorrente ao fluxo de produtoPrimeiros secadores eram dotados de ventiladores centrfugos, hoje quase todos os fabricantes utilizam ventiladores axiais
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Secadores em cascata ou de calhas
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Secadores em cascata ou de calhasProduto a ser seco deve apresentar baixo teor de impurezas caso contrrio o fluxo de produto pode tornar-se desuniforme
Existe um limite abaixo do qual o fluxo de produto no pode ser reduzido
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 contnuo apenas quando a umidade inicial igual ou inferior a 18%
Para melhorar a eficincia energtica os secadores passar a serem fabricados com opo de reaproveitamento do ar de resfriamento e de exausto
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Secadores de Calhas
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Secador tipo cascatacom reproveitamento do ar de resfriamento esistema de coleta departculas
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Secadores em cascata ou de calhasTemperaturas de secagemMilho e soja para consumo: 100o CTrigo para consumo: 70o a 80o CArroz: 70o a 80o CSementes: 50o a 60o C (no permitir os gros atinjam temperaturas superiores a 43o C
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Secadores de fluxos cruzadosSecador mais usado no mundo
Configurao, construo e operao simples
Passagem do ar perpendicular passagem dos gros que se movem entre duas chapas perfuradas
Espessura da camada de gros: 20 a 30 cm
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Secadores de fluxos cruzadosSecador convencional: problemas com gradiente de umidade e elevado consumo de energia
Para melhorar desempenho: reverso do fluxo de ar e reverso da camada de gros para reduzir o gradiente de umidade na camadareaproveitamento do ar de exausto para reduzir o consumo de energia
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Secador de fluxos cruzadosEsquema bsico
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Secadores de fluxos cruzados
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Secadores de fluxos cruzados
Secador modular permitindo diferentes configuraes para obteno de diferentes capacidades de secagem.
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Secadores de fluxos cruzados
Eclusas prximas entradade ar descarregam o produto mais rpido para reduzir ogradiente de umidade na camada.
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Recirculao do ar
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Secadores de fluxos concorrentesAr e gros fluem no mesmo sentido
Altas taxas de evaporao ocorrem na parte superior da camada, uma vez que o ar mais quente encontra o gro mais mido
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 geralmente feito em fluxos contracorrentes
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Secadores de fluxos concorrentes
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Secadores de fluxos concorrentes
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Secadores de fluxos concorrentes Vantagens:Melhor qualidade final do produtoMaior capacidade de secagem.Alta eficincia energtica.Baixo custo de instalao e manuteno
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Secadores de fluxos contracorrentesO ar de secagem e gros fluem em sentido contrrio.A frente de secagem permanece sempre prxima ao fundo perfurado. medida que o produto desce, sua temperatura aumenta, ficando prximas temperatura do ar de secagem.A temperatura de secagem no deve ultrapassar 70oC.
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Secadores intermitentesProduto ao passar pelo secador retorna parte superior do secador
Quando dotados de cmaras de repouso geralmente o produto permanece 10% na cmara de secagem e o restante do tempo na cmara repouso
Cmaras de repouso: melhor eficincia energtica e melhor qualidade do produto final
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Secadores intermitentes
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Secagem em combinaoSecagem em altas temperaturas at o produto atingir 16% a 18% de umidade
Secagem em baixas temperaturas no final do processo de secagem
Melhor eficincia energtica e melhor qualidade do produto final
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Seca-aerao
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Seca-AeraoAumento da capacidade de secagem do secador: 50% a 75%
Reduo do consumo de energia: 20% a 40%
Melhoria da qualidade do produto final
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