Numerical investigation of the interstage backmixing in multistage compartmented agitated column with single phase

Multistage compartmented agitated column (MSAC) is widely used in extraction and chemical reaction. Interstage backmixing determines reactor performance, which is controlled by open channel area and its attaching draft tube in divider stage. However, the relation between backmixing and flow pattern condition within different internal structures and impeller types is still confused. In this work, the backmixing characteristics in a four stage MSAC have investigated, in order to explore the effect of opening channel radial position, draft tube direction and impeller type. The flow condition especially for backmixing in MSAC is simulated by CFD. The backmixing intensity in each case is determined based on the simulated RTD normalized variance. Results show that the variation of backmixing intensity is clarified with the analysis of circulation loop flow pattern, flow resistance, mixing intensity and impeller feature. The backmixing rate decreases first and then increase along the radial position, which has controlled by the fluid circulation loop. The backmixing rate reduced with the adding of draft tube due to the increasing flow resistance. Furthermore, strong mixing lead to higher backmixing intensity, and the axial flow impeller features with large backmixing intensity under unit stirring powder density.