Scaling up bubble column reactors with the aid of CFD

Abstract

Bubble column reactors, used widely in industry, often have large column diameters (up to 6 m) and are operated at high superficial gas velocities (in the range of 0.1 to 0.4 ms⁻¹) in the churn-turbulent flow regime. Experimental work on bubble column hydrodynamics is usually carried out on a scale smaller than 0.3 m, at superficial gas velocities lower than 0.25 ms⁻¹. The extrapolation of data obtained in such laboratory scale units to the commercial scale reactors requires a systematic approach based on the understanding of the scaling principles of bubble dynamics and of the behaviour of two-phase dispersions in large scale columns. We discuss a multi-tiered approach to bubble column reactor scale up, relying on a combination of experiments, backed by Computational Fluid Dynamics (CFD) simulations for physical understanding. This approach consists of the following steps: (a) description of single bubble morphology and rise dynamics (in this case both experiments and Volume-of-Fluid (VOF) simulations are used); (b) modelling of bubble-bubble interactions, with experiments and VOF simulations as aids; (c) description of behaviour of bubble swarms and the development of the proper interfacial momentum exchange relations between the bubbles and the liquid; and (d) CFD simulations in the Eulerian framework for extrapolation of laboratory scale information to large-scale commercial reactors.