Using tomography and computational fluid dynamics to study the performance of a maxblend impeller for solid-liquid mixing operations

Prakash Mishra

doi:10.32920/ryerson.14644620

Abstract

A thorough literature review suggests that no comprehensive research work has been done regarding the characterization of the local solid concentrations in a slurry reactor equipped with a Maxblend impeller. The aim of this research work was to assess the mixing performance of a Maxblend impeller in a slurry reactor through electrical resistance tomography (ERT) and computational fluid dynamics (CFD). The mixing efficiency of the Maxblend impeller for solid-liquid mixing operation was compared to those measured for the A200 (an axial-flow impeller) and the Rushton turbine (a radial-flow impeller). The tomography images were employed to assess the particles distribution inside the slurry reactor. The CFD model was created using the Eulerian and Eulerian (E-E) method, standard k-ε turbulence model, and sliding mesh (SM) technique for simulating the two-phase fluid flow, turbulence effects, and stirrer rotation, respectively. The validated CFD model was utilized to obtain the particle concentration profiles and to determine the local particle distributions attained by the Maxblend impeller. The data were utilized to analyze the impacts of various important parameters such as the agitation speed, particle concentration, particle diameter, specific gravity of the particle, and the use of baffles on the mixing efficiency of the Maxblend impeller in terms of the extent of homogeneity and mixing index. The particle distribution in the slurry reactor furnished with a Maxblend impeller was also assessed through clouding height and just suspended agitation speed approaches in this study. The results from this study showed that the assessment of the optimum impeller speed is extremely important to enhance the local mixing quality in the mixing vessel. Experimental tests demonstrated that maximum homogeneity attained by the Maxblend impeller was higher than those for the A200 and Rushton impellers.

Highlights

It is generally accepted that mixing processes play a vital role for commercial success of a process industry because of extensive use of mixing in various unit operations
It is imperative to mention that the validation of the generated computational fluid dynamics (CFD) model was done by comparing the results obtained from the simulation to experimental data in terms of stirrer torque, just suspension speed (Njs) and the degree of homogeneity. 5.2.1 Qualitative Validation
The generated CFD model was validated and verified by comparing the results obtained from the simulation to the experimentally determined values in terms of the stirrer torque, just suspension speed, and extent of homogeneity

Summary

Introduction

It is generally accepted that mixing processes play a vital role for commercial success of a process industry because of extensive use of mixing in various unit operations. Solid-liquid mixing operation is one of the most pivotal mixing operations because of its wide range of utilizations in several unit processes and operations. Stirred tanks are employed for various purposes such as maximizing homogeneousness of the system taking concentration gradients into considerations (Tatterson, 1991), and improving mass transfer among the different phases. Sometimes understanding the parameters affecting the mixing processes can be complicated due to the number of variables involved (Tatterson, 1991). The main goals of mixing operation in solid-liquid system are (Mak, 1992): (a) to prevent settling of particles in an agitated vessel, (b) to improve the mass transfer between two phases by increasing surface areas for the contact between the liquid and solid particles, and (c) to ensure the uniform dispersion and distribution of particles throughout the mixing tank

Methods

Results

Conclusion