Fermenters concentric tube airlift

Fig. 2 Concentric tube airlift fermenters (A) draft-tube sparged and (B) annulus sparged. (View this art in color at www. dekker.com.)...

The focus of this entry is limited to the design of aerobic fermenters, i.e., stirred tank and concentric tube airlift fermenters, which are commonly utilized in the bioprocessing industries. Design principles and the basic calculations are described with a couple of industrial examples. Readers with a limited background in mixing technology are referred to the gas-liquid contactor entry of this encyclopedia for a more comprehensive understanding of fluid flow and mass transfer characteristics in stirred tank reactors and bubble columns. 

This, the second of two fermenter design examples, deals with a concentric tube airlift fermenter. Non-dimensional parameters applicable in this example are defined as follows. 

The following nondimensional mass transfer correlation, represented by the Sherwood number, is valid for the draft-tube sparged concentric tube airlift fermenter. ... 

Kawase, Y, and Moo-Young, M. (1986b), Mixing and mass transfer in concentric-tube airlift fermenters Newtonian and non-Newtonian media, Journal of Chemical Technology and Biotechnology, 36(11) 527-538. 

A 2 IB. Braun airlift fermenter with a working volume of about 2000 ml was used. Sterile air is sparged through a sintered plate located near the bottom of the central concentric tube. There was no mechanical stirring only the air nozzle was forced through the centred tube and the flow directed to the annulus tube side. Aeration causes circulation of media the flow is gentle without serious shear forces. The temperature is maintained at 26 °C. 

The airlift fermenter relies on air as the principal means of achieving various transport requisites. It is composed of a vertical cylindrical vessel and a concentric draft tube into which air or other suitable oxidation gases are injected (see Fig. 2). Reduced bulk density causes the contents of the central riser to move upward. This action displaces the contents of the... 

The design of a concentric tube internal loop airlift fermenter for the production of a biocatalysis enzyme at an annual rate of 8000 5%kg/yr is illustrated below. Product recovery efficiency is 80% and the titer... 

Phenoloxidase (monophenol monooxygenase, E.C. 1.14.18.1) introduces one atom of molecular oxygen into the substrate and was used in alginate-entrapped cells or in partially purified form. The pharmaceutical 7,8-dihydroxy-N-(di-n-propyl)-2-aminotetralin was produced continuously using a phenol oxidase suspension in dialysis tubing in an airlift fermenter coupled to an aluminium oxide column for selective product isolation (Figure 16.3-13)[6S1. A product concentration of 130 mg/L and a yield of 25 % were reached. 

In airlift bioreactors the fluid volume of the vessel is divided into two interconnected zones by means of a baffle or draft-tube (Fig. 5). Only one of these zones is sparged with air or other gas. The sparged zone is known as the riser the zone that receives no gas is the downcomer (Fig. 5a-c). The bulk density of the gas-liquid dispersion in the gas-sparged riser tends to be less than the bulk density in the downcomer consequently, the dispersion flows up in the riser zone and downflow occurs in the downcomer. Sometimes the riser and the downcomer are two separate vertical pipes that are interconnected at the top and the bottom to form an external circulation loop (Fig. 5c). External-loop airlift reactors are less common in commercial processes compared to the internal-loop designs (Fig. 5a, b). The internal-loop configuration may be either a concentric draft-tube device or an split-cylinder (Fig. 5a, b). Airlift reactors have been successfully employed in nearly every kind of bioprocess—bacterial and yeast culture, fermentations of mycelial fungi, animal and plant cell culture, immobilized enzyme and cell biocatalysis, culture of microalgae, and wastewater treatment. 

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