A Study On Solid-Liquid Suspension In A Stirred Tank With Draft Tube

A stirred tank with draft tube is a very common apparatus in the chemical industry and is widely used in many industrial processes. For the design of draft-tube stirred tank, it is important to study the effect of the structure of draft-tube stirred tank on particle off-bottom suspension.The mixing characteristics of two phases (solid-liquid) in a stirred tank of0.8m diameter with draft tube were investigated experimentally. The experimental investigation was carried out in the shallow conical bottom, cylindrical vessel, with0.8m diameter, equipped with a new type propeller-three blade hydrofoil (WHD-1) with a diameter of0.2m,0.256m and0.32m to push the water downward. Water was used as liquid phases, glass beads of a diameter of (p=2500Kg·m-3) dp=100μm、525μm、900μm and the resin particles of (p=1500Kg·m-3) dp=400μm、700μm were used as settling particles. Power number and circulation flow number were investigated in a draft-tube stirred tank with different structure. The particle distribution in the tank was measured with the infrared nephelometer GD-11and the off-bottom suspension in the whole tank was researched. Power number and circulation flow number in draft-tube stirred tank with different structure was investigated. The solid concentration distribution in a draft-tube stirred tank of0.8m diameter were experimentally studied and numerically simulated by using computational fluid dynamics (CFD) package CFX. The circulation flow number and solid concentration distribution predicted by CFD were in good agreement with the experimental. The results are of importance to the optimum design of industrial stirred tank with draft tube.The results show that the diameter of draft tube and the off-bottom distance of draft tube affect circulation flow number and critical just off-bottom suspension impeller speed. When the CD=150mm-170mm, the critical just off-bottom suspension impeller speed was the least. The draft tube (0.20T) was better than the draft tube (0.32T,0.40T),when the solid phase was off-bottom suspension. The draft tube (0.40T) was better than the draft tube (0.25T,0.32T), when the solid particle was homogeneous suspension.