In this work, the influence of addition of normal aliphatic alcohols (from methanol to n-octanol) and the gas sparger type (single orifice, perforated plate, and sinter plate) on the volumetric mass transfer coefficient in a draft tube airlift reactor was investigated. The results showed that the addition of alcohols from methanol to n-hexanol led to an increase in the volumetric mass transfer coefficient, in comparison to water, while n-heptanol and n-octanol had the opposite effect. The influence of the gas sparger was dominant at low superficial gas velocities. At higher gas velocities, the liquid-phaseproperties and the sparger type, being opposite in effect on mass transfer, annulled one another's influence. Also, simple correlation was proposed to predict the volumetric mass transfer coefficient. The analysis of the parameters in the proposed correlation showed that the liquid-phaseproperties, expressed through the surface tension gradient, and the gas sparger type, mainly through initial bubble size, had a marked influence on the mass transfer.
The influences of alcohol adding and three different gas spargers (single orifice, perforated plate, and sinter plate) on the gas holdup in an external-loop airlift reactor were studied. The experimental results show that the gas holdup can be increased by mutual influence of both the alcohol adding and the sparger type. The presence of small amounts of normal aliphatic alcohols caused an increase of the gas holdup compared to the air-water system, due to their coalescence-inhibiting nature. The sinter plate was the most efficient sparger, followed by the perforated plate and the single orifice. A proposed artificial neural network (ANN) has the potential to predict gas holdup values in airlift reactors for various alcohols and types of gas spargers.
The objective of this work was to investigate the influence of normal aliphatic alcohols (from methanol to n-octanol) and the gas sparger type (single orifice, perforated plate, and sinter plate) on the hydrodynamics of a draft tube airlift reactor. The results showed that the presence of alcohols led to both an increase in the gas holdup and reduction of the downcomer liquid velocity, in comparison to the values obtained in water. The type of gas sparger also changed the hydrodynamic behaviorthe gas holdup increased with dispersion effectiveness, from single orifice to sinter plate, while the effect on the downcomer liquid velocity was in conjunction with the liquid phase properties. Simple correlations were developed to predict the gas holdup and the downcomer liquid velocity. Beside the gas superficial velocity, the proposed correlations include the surface tension gradient, as a unique parameter which represents the liquid phase properties, and sparger related variables: the ratio of the sparger’s total openings area and the draft tube cross-sectional area and also orifice (pore) size of the sparger.
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