Mixing Suspensions in Slender Tanks

F Rieger,E Rzyski

doi:10.14311/332

Abstract

Industrial suspension mixing processes are carried out both in standard tanks (H/D =1) and in the tanks with height H/D > 1. When only one impeller is used in such slender tanks, it may be difficult to produce a suspension of desired homogeneity. Hence it may be necessary to install a larger number of impellers on the shaft.The aim of this study was to explain the mechanism of suspension formation in slender tanks (H/D = 2) with an increased number of impellers. On the basis of the solid bed height on the tank bottom, the position of the suspension - water interface and the concentration profile of solid particles in the suspension (standard deviation of solid body concentration) the operation of the impellers was estimated and conclusions were drawn on how and at what distance from each other to install them were presented.The location of the upper, highest impeller appeared to be specially significant. On the basis of this study it is recommended to locate the upper impeller so that its distance from the free liquid surface is less than 0.8 D. It was found that such a position of the highest impeller was also advantageous from the energy point of view.

Highlights

In the chemical and food industry, the aim of mixing is often to obtain a solid suspension
At rotation frequency n = 200 min-1 solid particles are introduced into the suspension
Though all solid particles are in the suspension, and the level of separation reaches the height of the liquid in the tank, there are differences in the concentration, and the suspension is not homogeneous

Summary

Introduction

In the chemical and food industry, the aim of mixing is often to obtain a solid suspension. High homon geneity of the produced suspensions is required [1]. For mixing suspensions, both standard slender tanks of H/D = 1 and tanks with higher H/D ratios are used. It may be difficult to obtain the desired homogeneity of the suspension 0.2·d impeller or in the case of coarse grained suspensions) so it will be necessary to install more impellers on the shaft. The aim of this study is to explain the process of producing suspensions in slender tanks (H = 2D) equipped with one or more impellers

Objectives

Results

Conclusion