CFD simulation of internal air lift reactors: Design optimization

Abstract

Air-lift reactors are widely used in the chemical and biochemical process industries as efficient contactors for mass and heat transfer. Their main advantages are simple mechanical design, low shear rate, high capacity, good mixing, absence of mechanical agitators and low cost. The design and scale-up of these reactors require accurate information about the gas–liquid flow dynamics and is still poorly understood because of the complexity of the flow patterns and their unknown behavior under different sets of design parameters. The optimization methodology and its coupling with computational fluid dynamics (CFD) is presented. The Eulerian–Eulerian approach with two fluid models is used. The interfacial forces (drag and added mass force) between the phases are considered. Further, statistical analyses are used in order to maximize the understanding of the physical phenomena and optimal designs are searched by means of the multi-objective optimization using response surface method (RSM). Three different response surface models are investigated. A strategy for optimization is presented with five geometrical input parameters that are varied in between specified upper and lower bounds to optimize the liquid velocity and gas hold-up. The optimal geometrical design parameters for air-lift reactor have been recommended.