Modelling of air-lift fluidized bed: optimization of mass transfer with respect to design and operational parameters

Abstract

Biological three-phase reactions are conventionally carried out in bubble columns, stirred contactors or fluidized beds. New bioreactors and fermenters used for production or waste water treatment include ICI deep shaft aerators or internal draft-tube air-lift loop reactors and draft-tube fluidized beds. The fluidized beds have higher productivity than the continuous stirred type and there is no wash out or stratification of biomass. The three-phase fluidized bed has high power requirements and adequate data are not available for design of large-scale equipment. It is proposed to use an external loop air-lift reactor as an air-lift fluidized bed (ALFB), by fluidizing the light particles in the downcomer. The proposed ALFB is expected to have lower shear stress levels and has a high degree of design flexibility. The effect of design and operational parameters were simulated for an air-water system for an ALFB of 100 m³. Recommendations have been made for optimum mass transfer performance and suitable scale up criteria have been developed. The proposed ALFB has been shown to be more promising than the three-phase fluidized bed.