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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