Suspension quality and power consumption of the complex multiphase flow field in a draft-tube stirred reactor

Abstract Experiment and simulation were used to study the flow fields of a liquid–solid–solid three-phase system in a draft-tube stirred reactor with a six-flat-bladed turbine impeller (BT) and a 45° pitched six-bladed upflow turbine impeller (PBTU45). The computational fluid dynamics (CFD) formulation was based on a 3D Eulerian multi-fluid model along with a renormalization group (RNG) k-e turbulence model, which took into account the inter-phase momentum exchange between different phases. The CFD model was validated using experimental data, and the suspension quality was validated by determining the standard deviation of the solid concentration. Good solid suspension was achieved in flow fields agitated by the BT impeller at low impeller speeds. The draft tube adversely affected solid dispersion at most impeller speeds. In flow fields agitated by the PBTU45 impeller, good solid suspension required a faster impeller speed. The suspension quality with the draft tube was better than that without the draft tube under most operating conditions. The power consumption of the BT or PBTU45 impeller with the draft tube was less than that without the draft tube at most impeller speeds.