Characteristics of Local Flow Dynamics and Macro-Mixing in Airlift Column Reactors for Reliable Design and Scale-Up

Abstract

There has been tremendous development within mixing operations in industry. Incomplete knowledge of this process caused serious economic losses to process industries. For optimum yields and the economic potential that goes with better understanding of mixing, research in this field continues to grow. The major forms of mixing in industry are either by mechanical or pneumatic agitation. Airlift bioreactors achieve mixing through pneumatic agitation and have gained attention over two decades for their fluid dynamic characteristics and low power consumption. It has been widely applied in bioprocess industries for production of biochemicals, to wastewater treatment in which the performance of this reactor has been overwhelming with respect to its production levels as compared to the conventional mechanical agitation.In this review, mixing through mechanical and pneumatic agitation is compared. An extensive literature is distilled from various investigators on the hydrodynamics and mixing characteristics of airlift bioreactors. This review has emphasis on factors that affect mixing such as the geometrical parameters of the vessel, gas flow rate, properties of the liquid medium, sparger design and measuring techniques employed. In an attempt to understand process related issues, sophisticated advances in the measuring techniques provides more insight into mixing in this reactor. Thus extensive correlations have been proposed by various investigators to predict the hydrodynamic and mixing parameters. Some design modifications proposed by several scholars have also been reviewed.

Bubbly flow in an airlift column: a CFD study

“…Thorough validation of these closure models is a cornerstone on the way to achieving reliable predictions. A complete model is very complex comprising the processes of mixing, mass transfer, metabolism, and for phototrophic organisms in addition light transmission coupled to the fluid dynamics. To obtain reliable results in this situation each part of the model has to be validated individually.…”

Dynamic and local gas holdup studies in external loop recirculating airlift reactor with two rolls of fiberglass packing using electrical resistance tomography

“…This class of bioreactors is divided into two main subclasses of internal and external loop airlift bioreactors. The main difference in the design of the external loop airlift bioreactors is that the liquid circulation in the riser and downcomer takes place in two separate compartments, which are connected by a pipe at the bottom and a pipe or a tank at the top . This design leads to maximum deaeration in the gas disengagement section of the external loop airlift bioreactors.…”

“…This develops a difference in density and hydrostatic pressure in the riser and downcomer, which results in lower gas recirculation and higher liquid circulation. This consequently enhances mixing and heat transfer in the bioreactor , , , …”

A method of short-circuiting comparison with mixing indexes

“…Consequently, it's possible to do the evaluation on short-circuiting by mixing indexes. There are numerous papers focusing on mixing doi: 10.2166/aqua.20tl.ll9 characteristics (Dusting & Balabani 2009;Gumery et al 2009;Sardeshpande et al 2009;Zhang et al 2009a), index dynamics (Smith et al 1993;Teixeira & Siqueira 2008;Siiriä & Yliruusi 2009), blender effect (Mehrotra & Muzzio 2009) and reactor performance (Bedoya et al 2009;Zhang et al 2009b).…”