Gas Dispersion and Solid Suspension in a Three-Phase Stirred Tank With Multiple Impellers

Abstract

Despite much research on gas-liquid-solid systems and their widespread application in industry, gas dispersion with solid suspension in multistage stirred reactors equipped with multiple impellers has received little attention. We report here the critical just-suspension impeller speed for different concentrations of solid particles, gas holdup, and shaft power in a vessel of 0.48 m diameter with four baffles and dished base. Five agitator configurations, each with three impellers mounted on a single shaft, have been used in the experiments. Two novel impeller designs were used, a deep hollow blade (semi-ellipse) disc turbine (HEDT) and four-wide-blade hydrofoil impellers. The hydrofoils were used in both up-pumping (WH U ) and down-pumping (WH D ) modes. Glass beads of 50 $ 150 lm diameter and density 2500 kg Á m À3 were suspended at solid volumetric concentrations of 1.5, 3, 6, 9, and 15%. Results show that these suspended solids have little effect on the relative power demand. Agitators using the HEDT radial dispersing impeller at the bottom have a higher relative power demand (RPD ¼ P G =P U ) than those with WH D or WH U as the lowest one. For all impeller combinations there is little or no effect on gas holdup with increasing solid concentrations. Of the five different impeller combinations, those with an axial flow bottom impeller have significantly higher just-suspension agitation speeds and power consumption, so mounting the hydrofoil impeller at the bottom is not the optimal configuration for particle suspension. Of these impeller combinations, at a given gas flow rate the arrangement of HEDT þ 2WH U has the highest relative power demand, gas holdup, and power input for both the suspension of settling particles and gas dispersion.

Use of acoustic emission in combination with machine learning: monitoring of gas–liquid mixing in stirred tanks

“…The presence of solids will cause an increase in the emitted signal because of impacts of the particles with the wall, the impeller and with each other, but the system will be challenged to correctly predict the gas-liquid operating regime. The regime is considered unchanged at fixed air volumetric flow and impeller speed: for low concentration [< 20% w/w (Chapman et al 1983b)] of solids, works in the literature report little effects of the presence of the particles on the gas sparging dynamics (Bao et al 2006;Chapman et al 1983b).…”

Local and overall gas holdup in an aerated coaxial mixing system containing a non‐Newtonian fluid

“…Radial flow impellers resulted in a poor distribution of gas throughout the system even in multi‐impeller configurations such as a system with three Rushton turbines 15 . However, Bao et al 16 reported that a combination of a radial and an axial flow impeller resulted in a better gas distribution due to the radial impeller's high energy dissipation rate. Among radial impellers, the Scaba impeller has shown some promising characteristics in both single and multiphase systems as well as coaxial systems 17 .…”

Mass Transfer Prediction in a Mechanically Stirred Gas‐Liquid Reactor Containing Solid Particles

“…Multiple authors also reported a small or no effect of the solid phase on the volumetric mass transfer coefficient 11–13. The increasing industrial importance of gas‐liquid‐solid systems has led to a focussed interest on the solid phase influence in such systems during the last couple of years 4, 14, 15. However, the mass transfer in gas‐liquid‐solid systems has not been fully described and understood, yet.…”