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

Abstract

A 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 (k L a) 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 (A r /A d ) and the superficial gas velocity in the riser (U g ) when deoxidized distilled water was used as the oxygen absorbent. An oxygen transfer rate of (2.17 ± 0.11) × 10 À5 kg m À3 s À1 , k L a of (27.88 ± 1.12) × 10 À3 s À1 and gas holdup of 0.031 were obtained with the ILAR of A r /A d = 1.09 and h/H = 0.73 at U g = 18 mm s À1 . 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 k L a 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 (V R ) and falling velocity in the downcomer (V D ) may be expressed by power-law functions of U g and A r /A d , 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.

Two-Phase Flow Mass Transfer Analysis of Airlift Pump for Aquaculture Applications

“…Another method of changing the airlift system design that could affect the oxygen transfer coefficients is by adjusting the riser pipe diameter or shape. In a study conducted by Pi et al [21], the idea of a trumpet-shaped riser was investigated. This trumpet-shaped riser was placed inside an airlift reactor where it could act as a modified internal-loop reactor [21].…”

“…In a study conducted by Pi et al [21], the idea of a trumpet-shaped riser was investigated. This trumpet-shaped riser was placed inside an airlift reactor where it could act as a modified internal-loop reactor [21]. From the experiments performed, the volumetric oxygen transfer coefficient was greatly influenced by the ratio of riser height to the static fluid head above the spargers, the ratio of the area of the cross-section of the riser to the downcomer (Ar/Ad) and the superficial gas velocity within the riser [21].…”

“…This trumpet-shaped riser was placed inside an airlift reactor where it could act as a modified internal-loop reactor [21]. From the experiments performed, the volumetric oxygen transfer coefficient was greatly influenced by the ratio of riser height to the static fluid head above the spargers, the ratio of the area of the cross-section of the riser to the downcomer (Ar/Ad) and the superficial gas velocity within the riser [21]. This uniquely formed riser provided optimal conditions for fluid circulation which enhanced the efficiency of the oxygen transfer and an oxygen transfer rate of (2.17 ± 0.11) × 10 −5 kg m −3 s −1 was recorded with an oxygen mass transfer coefficient of (27.88 ± 1.12) × 10 −3 s −1 [21].…”