Influence of Sparger Type on Mass Transfer in a Pilot-Scale Internal Loop Airlift Reactor

Zongliang Wang,Zibin Huang,Hongshan Guo,Tong Zhou,Zhenmin Cheng

doi:10.3390/pr10020429

Abstract

In a pilot-scale internal loop airlift reactor with a height of 5.5 m and a main column diameter of 0.484 m, the influence of three gas sparger structures (ladder distributor, tri-nozzle sparger and perforated plate) on the volumetric mass transfer coefficient kLa was investigated. It was found that the perforated plate produces the highest gas holdup difference and circulating liquid velocity between the riser and the downcomer. The perforated plate provides the most efficient mass transfer due to the more uniform gas distribution and higher circulating liquid velocity, followed by the ladder distributor and tri-nozzle spargers. Compared with the tri-nozzle sparger, the perforated plate increases the value of kLa by up to 16% at a superficial velocity of 0.15 m/s. Interestingly, the analysis of the liquid-phase mass transfer coefficient kL and specific area a with respect to gas velocity shows that the mass transfer rate is primarily controlled by a. By comparing the predictions of different mass transfer models, the slip velocity model based on penetration theory yields a satisfactory agreement with the experimental results within ±15% error. Meanwhile, empirical correlations regarding gas holdup and kLa were developed and were found to have good consistency with experimental values.

Highlights

Airlift reactors are extensively employed as multiphase reactors in biochemical, petrochemical and wastewater treatment industries due to their simple design, easy operation, low power consumption, lack of moving parts and good heat and mass transfer rates [1,2]
Naidoo et al [6] investigated the effects of sparger type on the gas holdup and mass transfer characteristics in an external loop airlift reactors (ELAR), finding that the sparger design strongly affected the holdup and mass transfer coefficient
Wei et al [7] measured the hydrodynamics and kLa in an internal loop airlift reactors (ILAR) equipped with two gas spargers, concluding that the bioreactor using the membrane-tube sparger increased the values of gas holdup, liquid circulation velocity and mass transfer coefficient in an air–water system compared with the perforated plate sparger

Summary

Introduction

Airlift reactors are extensively employed as multiphase reactors in biochemical, petrochemical and wastewater treatment industries due to their simple design, easy operation, low power consumption, lack of moving parts and good heat and mass transfer rates [1,2]. Šijacki et al [8] conducted experiments to measure mass transfer coefficient in an ILAR with three different gas spargers: single orifice, perforated plate and sinter plate. They found that the sparger type had a marked influence on the primary gas dispersion and kLa. Luo et al [9] studied the influences of sparger design on the hydrodynamics and kLa in an ILAR. Ham et al [10] investigated the effect of three types of spargers (commercial fine sand and coarse sand diffusers, and perforated diffusers with different orifice sizes) on bubble hydrodynamics and mass transfer performance in bubble column and airlift reactors.

Experimental Apparatus and Methods

Gas Holdup

Circulating Liquid Velocity

Influence of Axial and Radial Positions

Findings

Conclusions