Power Consumption, Axial Oil Phase Distribution and Gas Holdup in a High-Aspect-Ratio Stirred Vessel with a Gas-Liquid-Liquid System

Cold model experiments were carried out in a high-aspect-ratio stirred vessel to investigate the effects of aeration on power consumption, axial oil phase distribution and gas holdup in a gas-liquid-liquid system under a nominal transitional flow regime. A mixed Fischer-Tropsch α-olefin/1,2-propanediol liquid-liquid system with an initial volume ratio of 1:1 was used, and air was introduced into a three-stage impeller configuration at a liquid height-to-tank diameter ratio of H/T = 2.10. The stirring speed ranged from 130 to 300 r·min⁻¹, corresponding to a nominal impeller Reynolds number of 2827 to 6524. The results showed that aeration reduced both the relative power consumption and the net power input per unit liquid volume, with a maximum relative power reduction of about 28.4%. When the gas flow rate exceeded 40 L·min⁻¹, the additional power reduction became limited. Increasing the stirring speed reduced the axial difference in local oil phase volume fraction, whereas further increasing the gas flow rate from 40 to 100 L·min⁻¹ did not lead to a continuous change in the axial oil phase distribution. The overall gas holdup generally increased with gas flow rate and stirring speed, but its increment was small when the gas flow rate increased from 60 to 80 L·min⁻¹ under stirred conditions. Considering power consumption, axial oil phase distribution and gas holdup, 40 to 60 L·min⁻¹ was identified as a suitable gas flow rate range under the present experimental conditions.