In this study, we use computational fluid dynamics (CFD) to characterize the flow of three different internal loop ALR geometries with different internal configurations (single and double draft tubes). Design parameter variations of the studied ALRs will allow the prediction of optimal configurations for bioreactors, e.g. in more efficient biorefinery concepts. No previous CFD studies have been found in literature comparing the flow of single stage and multi-stage internal loop ALRs. Higher mixing intensities were achieved in the upper part of the double stage internal loop ALR, the ratio between the bioreactor and the draft tube has an effect on the downcomer velocity.