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Mixing time and oxygen transfer characteristics of double draft tube airlift fermentor
Author(s) -
Margaritis Argyrios,
Sheppard John D.
Publication year - 1981
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.260230915
Subject(s) - draft tube , body orifice , sparging , airlift , mixing (physics) , concentric , mechanics , diameter ratio , jet (fluid) , tube (container) , volume (thermodynamics) , chromatography , chemistry , materials science , analytical chemistry (journal) , geometry , mechanical engineering , physics , bioreactor , thermodynamics , composite material , mathematics , engineering , organic chemistry , quantum mechanics
Despite the increasing importance of airlift fermentors, very little published information is available on how the geometric configurations of the draft tubes and the air‐sparging system affect the mixing and oxygen transfer characteristics of the fermentor. A 14‐L air‐lift fermentor was designed and build with a fixed liquid height to diameter ratio of 1.5 utilizing four equally spaced air jets at the bottom. Two jet orifice sizes were used, 1.27 and 3.81 mm i.d., and for each jet size the following four geometric configurations were used: Single inner concentric draft tube, single outer concentric draft tube, two concentric draft tubes, and no draft tubes where the fermentor was operated as a shallow bubble column. It was found that the presence of draft tubes stabilized liquid circulation patterns and gave systemically higher mixing times than those obtained in the absence of draft tubes. In addition, the double draft tube geometry resulted in higher mixing times than the single draft tubes. For the power unit volume range 20 to about 250 W/m 3 the larger 3.81‐mm orifices gave systemically higher k L a values than the smaller 1.27‐mm i.d. orifices. At 200 W/m 3 the use of a single outer draft tube with the 3.81‐mm orifices resulted in 94% increase in k L a values over that obtained with no draft tubes. However, the effect of draft tube geometry on k L a values when the 1.27‐mm orifices were used was not significant. The air bubble formation characteristics at the jet orifices were found to be different, which reflected the differences observed in mass transfer and mixing characteristics. The power economy for oxygen transfer was found to be depend strongly on the orifice size and less on the geometric configuration of draft tubes.