SECAGEM DE GROS EM ALTAS TEMPERATURASProf. Daniel Maral de Queiroz
Viosa, MGAgosto/2002
Classificao dos secadores quanto ao fluxo de produtoleito fixofluxos cruzadosfluxos concorrentesfluxos contracorrentesfluxos mistos
estacionrioscontnuosintermitentes
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
Secador de Camada FixaModelo UFV
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
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
Secador de leito fixo ou de camada estacionria - Top Dry
Secagem em leito fixo no topo do silo, resfriamento na parte inferior.
Secador de leito fixo ou de camada estacionria - com sistema de revolvimentoComponentes:Silo metlicoPiso plano perfuradoVentiladorAquecedorRevolvedor de grosEspalhadorSistema de descarga
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.
Secador de leito fixo ou de camada estacionria - com sistema de revolvimentoDetalhe dosistema derevolvimento
Secador de leito fixo ou de camada estacionria
Sistema utilizado no Brasil para secagem de amendoim.
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.
Conveco Natural
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
Secadores em cascata ou de calhas
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
Secadores de Calhas
Secador tipo cascatacom reproveitamento do ar de resfriamento esistema de coleta departculas
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
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
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
Secador de fluxos cruzadosEsquema bsico
Secadores de fluxos cruzados
Secadores de fluxos cruzados
Secador modular permitindo diferentes configuraes para obteno de diferentes capacidades de secagem.
Secadores de fluxos cruzados
Eclusas prximas entradade ar descarregam o produto mais rpido para reduzir ogradiente de umidade na camada.
Recirculao do ar
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
Secadores de fluxos concorrentes
Secadores de fluxos concorrentes
Secadores de fluxos concorrentes Vantagens:Melhor qualidade final do produtoMaior capacidade de secagem.Alta eficincia energtica.Baixo custo de instalao e manuteno
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.
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
Secadores intermitentes
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
Seca-aerao
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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