Cultivo em estado sólido em biorreator de tambor horizontal: modelagem, simulação e experimentação
Data
2020-04-16
Autores
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Universidade Estadual Paulista (Unesp)
Resumo
Esta tese apresenta um estudo sobre modelagem a uma fase de leitos estáticos em tambores horizontais construídos para cultivo sólido. Para tanto, balanços de massa foram propostos para leitos isotérmicos sem reação, seguidos de balanços de calor e massa para três dimensões de tambor: 10, 20 e 31 cm de diâmetro e 20, 40 e 74 cm de comprimento, respectivamente. Vazões de ar seco de 5 e 50 L/min foram assumidas para leitos compostos por sílica gel e por fibras de bagaço de cana. Balanços para a fase gasosa escoante foram também propostos e solucionados simultaneamente aos balanços para o leito. Propriedades efetivas de transporte foram determinadas experimentalmente e/ou calculadas. A convergência entre a difusividade efetiva de água em leito de bagaço de cana sugere sua representação preferencialmente através da dependência da umidade de partículas em ensaios com duração superior a dez horas. Para ensaios relativamente curtos, a dependência do parâmetro em relação à posição radial pode ser suficiente. Uma análise de Número de Biot modificado foi apresentada para transporte de massa adotando-se um fator de correção referente à posição no leito. Em sistemas isotérmicos, o transporte de massa é governado pela resistência interna a 50 L/min principalmente nos primeiros instantes de ensaio, evoluindo para resistências equivalentes ao longo do tempo; a resistência externa ao transporte de massa é predominante a 5 L/min. Balanços de calor e massa requereram as condutividades térmicas efetivas dos leitos de partículas, extraída da literatura para o leito de bagaço de cana e determinada experimentalmente com dependência explícita da temperatura e da umidade das partículas para o leito de sílica gel. Correlações foram utilizadas para estimativa das condutividades térmicas efetivas, obtendo-se bons resultados para o leito de sílica e resultados confiáveis apenas para uma faixa de umidade de partículas em leito de bagaço de cana, correspondente a até 0,43 kg/kg de sólido seco. Balanços de massa e energia para a fase gasosa no sobre espaço foram acoplados à solução dos balanços para o leito de partículas. Dentro dos três tambores, a temperatura do gás no sobre espaço pode ser assumida constante a 45 ºC, o gás não deixa os tambores em condição de saturação e perfis axiais de umidade são desenvolvidos. Quanto à transferência de calor em sistemas não isotérmicos, a parede do tambor é a principal fronteira através da qual o calor é transferido e as resistências internas ao transporte de calor são desprezíveis em tambor de 10 cm de diâmetro. O número de Biot de massa modificado foi calculado também para os sistemas não-isotérmicos e acusou ausência de resistências externas somente em leito de sílica gel para todos os tamanhos de tambores em vazão de 50 L/min. Nos demais leitos, tambores e vazões, resistências equivalentes governaram o transporte de massa. Os balanços de calor e massa foram adicionados de um termo que representa a geração de calor pelo microrganismo e foram validados utilizando-se a cinética de liberação de gases pelo fungo Myceliophthora thermophila l-1D3b em leito de bagaço de cana e farelo de trigo com suprimento de ar a 5 L/min e 96 e 75 % de umidade relativa, cujos picos de temperatura foram observados em 28 e 42 horas, respectivamente. Durante o cultivo, o controle de temperatura foi eficiente apenas em tambor com 10 cm de diâmetro, com elevações de temperatura de aproximadamente 3,5 e 7 ºC em tambores com 20 e 31 cm de diâmetro, respectivamente. Em tambor médio, mais intensa atividade metabólica foi observada quando gás foi inserido a 96 % de UR. As atividades enzimáticas de endoglucanase não foram afetadas pelos aumentos de temperatura, mas pelo ressecamento do leito. A temperatura do gás se aproximou da temperatura da superfície em todos os tambores e calor permaneceu acumulado no leito em tambor de 31 cm de diâmetro ainda ao final do cultivo. A boa concordância entre os perfis experimentais e fornecidos pelos modelos afirmam a sua aplicabilidade na predição de variáveis de interesse e podem ser empregados em estudos de aumento de escala de biorreatores para cultivo sólido.
The current work presents a study about one-phase modelling of static beds within horizontal drums built for solid-state cultivation. For this, mass balances were proposed for no-reactional isothermal beds, followed by mass and heat balances for three dimensions of drums: 10, 20 and 31 cm of diameter and 20, 40 and 74 cm of length, respectively. Dry airflow rates of 5 and 50 L/min were assumed for beds composed by silica gel and by fibers of sugar cane bagasse. Balances for the gas phase in the headspace were also proposed and simultaneously solved to the balances for the bed. Effective transport properties were experimentally determined and/or calculated. The convergence between the effective diffusivity of water in the bed of sugar cane bagasse suggests that its representation preferentially by the dependence on the moisture of the particles for experimental assays with duration higher than ten hours. For relatively short experimental assays, the dependence of the parameter on the radial position can be enough. An analysis of modified Biot number was presented for the mass transport adopting a correcting factor referent to the radial position in the bed. In isothermal systems, the mass transport is managed by the internal resistances at 50 L/min mainly in the initial instants of the test, evolving for equivalent resistances over time; the external resistance to the mass transport is predominant at 5 L/min. Mass and heat balances required the effective thermal conductivities of the beds, extracted from the literature for the bed of sugar cane bagasse and experimentally determined as dependence on the temperature and the moisture content of particles for the bed of silica beads. Correlations were used for estimative of effective thermal conductivities, obtaining satisfactory results for the bed of silica and confinable results only a range of moisture of sugar cane bagasse particles corresponding to up 0,43 kg/kg of dry solid. Mass and energy balances for the gas phase in the headspace were coupled to the solution of the balances for the bed of particles. For all the drums, the temperature of gas in the headspace can be assumed constant at 45 ºC, the gas does not leave the drums saturated of vapor of water vapor and axial profiles are developed. About the heat transfer in no-isothermal systems, the drum-wall is the main boundary through the heat is transferred and the internal resistances to the heat transfer are neglected within a drum of 10 cm of diameter. The modified Biot number for mass transfer was also calculated for no-isothermal systems and pointed absence of external resistances only for a bed of silica beads at 50 L/min for all the drums. For the others drums, beds and airflow rates, equivalent resistances managed the mass transport. Mass and heat balances were added of a term which represents the heat generated by the microorganism and validated using the kinetic of gas released by the thermophilic fungus Myceliophthora thermophila l-1D3b on a bed of sugar cane bagasse and wheat bran with air supplying of 5 L/min and 75 to 96 % of relative humidity, whose peaks of temperature were observed at 42 and 28 hours, respectively. During the cultivation, the controlling of temperature was efficient only within the drum of 10 cm of diameter, with increase of temperature of 3,5 and 7 ºC within drums with 20 and 31 cm of diameter, respectively. In the intermediary sized drum, more intense metabolic activity was observed when the gas was inserted at 96 % of RH. The enzymatic activities of endoglucanase were not be affected by the increase of temperature but the dryness of the bed was considered a critical condition. The temperature of the gas was close to the temperature of the surface in all the drums and energy kept accumulated in the bed of 31 cm of diameter also in the end of the cultivation process. The great agreement between the experimental profiles and those provided by the models affirm their applicability on the prediction of variables of interest and they can be employed in studies of scaling up of bioreactors for solid-state cultivation.
The current work presents a study about one-phase modelling of static beds within horizontal drums built for solid-state cultivation. For this, mass balances were proposed for no-reactional isothermal beds, followed by mass and heat balances for three dimensions of drums: 10, 20 and 31 cm of diameter and 20, 40 and 74 cm of length, respectively. Dry airflow rates of 5 and 50 L/min were assumed for beds composed by silica gel and by fibers of sugar cane bagasse. Balances for the gas phase in the headspace were also proposed and simultaneously solved to the balances for the bed. Effective transport properties were experimentally determined and/or calculated. The convergence between the effective diffusivity of water in the bed of sugar cane bagasse suggests that its representation preferentially by the dependence on the moisture of the particles for experimental assays with duration higher than ten hours. For relatively short experimental assays, the dependence of the parameter on the radial position can be enough. An analysis of modified Biot number was presented for the mass transport adopting a correcting factor referent to the radial position in the bed. In isothermal systems, the mass transport is managed by the internal resistances at 50 L/min mainly in the initial instants of the test, evolving for equivalent resistances over time; the external resistance to the mass transport is predominant at 5 L/min. Mass and heat balances required the effective thermal conductivities of the beds, extracted from the literature for the bed of sugar cane bagasse and experimentally determined as dependence on the temperature and the moisture content of particles for the bed of silica beads. Correlations were used for estimative of effective thermal conductivities, obtaining satisfactory results for the bed of silica and confinable results only a range of moisture of sugar cane bagasse particles corresponding to up 0,43 kg/kg of dry solid. Mass and energy balances for the gas phase in the headspace were coupled to the solution of the balances for the bed of particles. For all the drums, the temperature of gas in the headspace can be assumed constant at 45 ºC, the gas does not leave the drums saturated of vapor of water vapor and axial profiles are developed. About the heat transfer in no-isothermal systems, the drum-wall is the main boundary through the heat is transferred and the internal resistances to the heat transfer are neglected within a drum of 10 cm of diameter. The modified Biot number for mass transfer was also calculated for no-isothermal systems and pointed absence of external resistances only for a bed of silica beads at 50 L/min for all the drums. For the others drums, beds and airflow rates, equivalent resistances managed the mass transport. Mass and heat balances were added of a term which represents the heat generated by the microorganism and validated using the kinetic of gas released by the thermophilic fungus Myceliophthora thermophila l-1D3b on a bed of sugar cane bagasse and wheat bran with air supplying of 5 L/min and 75 to 96 % of relative humidity, whose peaks of temperature were observed at 42 and 28 hours, respectively. During the cultivation, the controlling of temperature was efficient only within the drum of 10 cm of diameter, with increase of temperature of 3,5 and 7 ºC within drums with 20 and 31 cm of diameter, respectively. In the intermediary sized drum, more intense metabolic activity was observed when the gas was inserted at 96 % of RH. The enzymatic activities of endoglucanase were not be affected by the increase of temperature but the dryness of the bed was considered a critical condition. The temperature of the gas was close to the temperature of the surface in all the drums and energy kept accumulated in the bed of 31 cm of diameter also in the end of the cultivation process. The great agreement between the experimental profiles and those provided by the models affirm their applicability on the prediction of variables of interest and they can be employed in studies of scaling up of bioreactors for solid-state cultivation.
Descrição
Palavras-chave
Modelagem e simulação, Tambor horizontal, Transferência de calor, Transferência de massa, Bagaço de cana, Cultivo em estado sólido, Modeling and simulation, Horizontal drum, Heat transfer, Mass transfer, Sugar cane bagasse, Solid-state cultivation