Experimental Investigation of Flow Development in Large-Scale Bubble Columns in the Churn-Turbulent Regime

Quantification of oxygen transfer coefficients in simulated hydrocarbon-based bioprocesses in a bubble column bioreactor

This study investigates the overall volumetric oxygen transfer coefficient (K_La) in multiphase hydrocarbon-based bioprocess under a range of hydrocarbon concentrations (H_C), solid loadings (deactivated yeast) (S_L) and superficial gas velocities (U_G) in a bubble column reactor (BCR). K_La increased with increasing U_G in the air-water system; due to an increase in the number of small bubbles which enhanced gas holdup. In air-water-yeast systems, the initial addition of yeast increased K_La significantly. Further increases in S_L reduced K_La, due to increases in the bubble size with increasing S_L. K_La decreased when H_C was added in air-water-hydrocarbon systems. However, U_G, S_L and H_C affected K_La differently in air-water-yeast-hydrocarbon systems: an indication of the complex interactions between the yeast and hydrocarbon phases which changed the system's hydrodynamics and therefore affected K_L. This work illustrates the effect of the operating conditions (S_L, H_C and U_G) on oxygen transfer behaviour in multiphase systems.

Prediction of Main Regime Transition with Variations of Gas and Liquid Phases in a Bubble Column

Industrial bubble columns mainly operate in a heterogeneous flow regime and identifying transition from homogeneous to heterogeneous flow is important. This work addresses the determination of flow regimes with gas-liquid systems in a bubble column. Various parameters of gas holdup, volumetric mass transfer coefficient, drift flux, and pressure standard deviations were investigated to precisely determine the superficial gas velocity at the transition regime. For a column aspect ratio (H/D: static liquid height to column diameter ratio) of 2.5 to 5, the transitional superficial gas velocity generally became higher with lower liquid height. However, the reverse trend was observed with a low density gas system due to the difference in force balance acting around the bubble. The weak body force and drag force in a lower axial position interrupted the mass transfer process. The experimental results showed similar ranges of the transitional superficial gas velocity regardless of the choice of parameter for detecting it. Because there is no precise correlation about transition regime properties, we proposed new correlations to predict both transition regime superficial gas velocity and gas holdup by taking the intersection of the two regimes. The correlations precisely captured the transition regime properties within 15% deviations even in gas-liquid systems that are not tested in this work.