Mixing performance of air-lift fermenters against working volume and draft tube dimensions

Sukan, Ş. Suha; Vardar‐Sukan, Fazilet

doi:10.1007/bf00369224

Cited by 19 publications

(7 citation statements)

References 5 publications

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“…1-7, 2-8). In this study the overall gas holdup was independent of draft tube height (1.11 m to 3.22 m) as observed previously by Russell et al [27] and Sukan and Sukan [33]. The improvement in liquid circulation with propeller operation at the shorter reactor height was of a similar magnitude to that with the tall vessel (Fig.…”

Section: The Effect Of Frequency Of Dot Changes On the Our Of The Baksupporting

confidence: 72%

Influence of a propeller on Saccharomyces cerevisiae fermentations in a pilot scale airlift bioreactor

Pollard

Ison

Shamlou

et al. 1997

Bioprocess Engineering

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The hydrodynamics (sectional gas holdup and liquid velocities) and oxygen transfer performance of a conventionally operated multiconfigurable pilot scale (0.25 m 3 ) concentric airlift bioreactor containing baker's yeast were significantly improved by operating a marine propeller to draw liquid down the draft tube and aid recirculation at the base of the vessel. Propeller operation reduced the severe DOT heterogeneity of the reactor, which gave DOT values below 1% air saturation in the riser, by producing DOTs above 40% around the vessel at maximum energy dissipation rate. As a consequence the overall oxygen uptake rate (OUR) of the baker's yeast increased up to 3 fold with the total energy dissipation rate into the reactor until the lowest DOTs of the vessel were at or above 10%. The different degrees of heterogeneity generated by the two reactor configurations enabled the reactor to be used as a scale down tool to study the impact of heterogeneity on the physiology of fermentation broths. Comparison of the hydrodynamics and oxygen transfer between tall and short reactor heights revealed that the faster circulation times of the short reactor produced a greater improvement in the OUR with propeller operation even though similar DOT changes occurred around both sizes of reactor. This indicated that the yeast cells were responding to the rapid DOT changes around the vessel. List of symbolsA D cross sectional area of the downcomer m 2 A R cross sectional area of the riser m 2 D p propeller diameter m DCW dry cell weight g/l DOT dissolved oxygen tension % air saturation g acceleration due to gravity m/s 2 H D height of the gas -liquid dispersion from the vessel base m H DT height of the top of the draft tube from the vessel base m k L a volumetric mass transfer coefficient s -1 L clearance between the bottom of the draft tube and vessel base m N propeller speed s )1 OUR oxygen uptake rate mmol/l.h P A energy dissipation rate for airlift aeration only operation W/m 3 P g energy dissipation for airlift operation W P IN pressure at the point of gas inlet to the vessel Pa P P energy dissipation rate for propeller only operation W/m 3 P O propeller power number -P T total energy dissipation rate for combined airlift and propeller operation W/m 3 t c liquid circulation time s t m mean mixing time to achieve 90% homogeneity s U LD mean liquid linear velocity in the downcomer m/s U LR mean liquid linear velocity in the riser m/s U sg superficial gas velocity in riser m/s V L liquid volume m 3 L density of liquid kg/m 3 w density of water kg/m 3 gas holdup -D mean downcomer gas holdup -O mean overall gas holdup -R mean riser gas holdup -TS mean top section gas holdup -1 Introduction Many studies of laboratory and pilot scale [7, 10, 22, 30] airlift reactors have considered the hydrodynamics and oxygen transfer but few have examined the impact of the circulatory flow on the metabolism of fermentation cultures. For airlift operation air is introduced into one section of the vessel and bubbles are entrained into the downcomer wh...

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Section: The Effect Of Frequency Of Dot Changes On the Our Of The Baksupporting

confidence: 72%

Influence of a propeller on Saccharomyces cerevisiae fermentations in a pilot scale airlift bioreactor

Pollard

Ison

Shamlou

et al. 1997

Bioprocess Engineering

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“…In the case of concentric-tube ALRs, the distance from the reactor base to the draft tube (bottom clearance) and the distance from the top of the draft tube to the top of the liquid level (top clearance) have received only minimal attention (Hwang and Fan, 1986; Sukan and Vardar-Sukan, 1987; Koide et al, 1984Koide et al, , 1988; Deng and Li, 1986).…”

Section: Introductionmentioning

confidence: 97%

Concentric‐tube airlift reactors: Effects of geometrical design on performance

Merchuk

Ladwa²,

Cameron³

et al. 1994

AIChE Journal

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Pressure drops, gas holdup, and mass-transfer coefficients were measured in two concentric-tube airlift reactors of 30 and 300 L (nominal volume). The aspect ratio and the ratio of riser to downcomer cross section were the same for both reactors, but the geometry of the gas separation section was different. The influence of the bottom and top clearances was studied using water and carboxymethyl cellulose solutions and covering a range of effective viscosity from 1O-j to 25 x 1O-j Pa-s. The pressure drop results expressed as a Euler number were satisfactorily correlated with Fr, Ga, and a bubble disengagement group M. Correlations are presented also for the gas holdup in the riser, downcomer, and gas separator. The last-mentioned coincides with the correlation for the total holdup in the reactor. The gas-liquid mass-transfer coefficients for all the liquids and geometric variables in both reactors were successfully correlated as Sherwood numbers.

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“…Liquid mixing has been shown to occur primarily in the head and bottom regions of the reactor, rather than via dispersion behind bubbles (Fields and Slater,1983;Weiland, 1984). Mixing times may be minimized by maintaining the unaerated liquid depth in the gas separation zone greater than one or two riser diameters (Fields and Slater, 1983;Sukan and Vardar-Sukan, 1987). Sparger design affects liquid velocities and mixing, particularly for small-scale reactors.…”

Section: Introductionmentioning

confidence: 99%