Oxygen mass transfer characteristics in an internal‐loop airlift reactor with preset trumpet‐shaped riser

Abstract

ABSTRACTA size‐adjustable trumpet‐shaped riser was installed into a conventional airlift reactor to form a modified internal‐loop airlift reactor (ILAR). The volumetric oxygen mass transfer coefficient (kLa) and gas holdup of the ILAR were heavily influenced by the height ratio of riser to static fluid level above the spargers (h/H), the cross‐sectional area ratio of riser to downcomer (Ar/Ad) and the superficial gas velocity in the riser (Ug) when deoxidized distilled water was used as the oxygen absorbent. An oxygen transfer rate of (2.17 ± 0.11) × 10−5 kg m−3 s−1, kLa of (27.88 ± 1.12) × 10−3 s−1 and gas holdup of 0.031 were obtained with the ILAR of Ar/Ad = 1.09 and h/H = 0.73 at Ug = 18 mm s−1. As the well‐constructed preset trumpet‐shaped riser provided ideal conditions for complete circulation and blending of the fluid, enhanced oxygen transfer efficiency was achieved. The gas holdup and kLa were increased by 16.2% and 10.2% at 19 °C, as compared with those of the conventional airlift reactor without this preset riser. The fluid rising velocity in the riser (VR) and falling velocity in the downcomer (VD) may be expressed by power‐law functions of Ug and Ar/Ad, respectively. These metrics indicate that the ILAR has better performance, as compared with a conventional airlift reaction, for oxygen transfer and microorganism culture for chemical engineering, biological fermentation and environmental protection. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.