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Effects of downcomer-to-riser cross sectional area ratio on operation behaviour of external-loop airlift bioreactors

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Abstract

Experiments performed in two external-loop airlift bioreactors of laboratory and pilot scale, (1.880–1.189) · 10−3 m3 and (0.170-0.157)m3, respectively, are reported. The A D /A R ratio was varied between 0.111–1.000 and 0.040–0.1225 in the laboratory and pilot contractor respectively.

Water and solutions of different coalescence (2-propanol 2% vol, 1 M Na (glucose 50% wt/vol) and rheological behaviour (non-Newtonian starch solutions with consistency index K=0.061–3.518 Pasn and flow behaviour index n=0.86-0.39), respectively, were used as liquid phase. Compressed air at superficial velocities v SGR =0.016–0.178 ms−1 in the laboratory contactor and v SGR =0.010–0.120 ms−1 in the pilot contactor, respectively was used as gaseous phase.

The A D /A R ratio affect gas-holdup behaviour as a result of the influence of A D /A R on liquid circulation velocity.

Experimental results show that A D /A R ratio affect circulation liquid velocity by modifying he resistence to flow and by varying the fraction of the total volume contained in downcomer and riser. A D /A R ratio has proven to be the main factor which determines the friction in the reactor. Mixing time increases with increasing of the reactor size and decreases with A D /A R decreasing.

The volumetric gas-liquid mass transfer coefficient increases with A D /A R ratio decreasing, as a result of variations of the liquid velocity with A D /A R , which affect interfacial areas.

Correlations applicable to the investigated contactors have been presented, together with the fit of some experimental data to existing correlation in literature.

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Abbreviations

A D :

downcomer cross sectional area (m2)

A R :

riser cross sectional area (m2)

a :

coefficient in Eq. (9) (-)

a L :

gas-liquid interfacial area per unit volume (m−1)

b :

coefficient in Eq. (9) (-)

C :

tracer concentration (kg m−3)

C ∞ :

tracer concentration at the state of complete mixing (kg m−3)

c :

coefficient in Eq. (12)

c S :

coefficient in Eq. (5)

D D :

downcomer diameter (m)

D R :

riser diameter (m)

d B :

bubble size (m)

H D :

downcomer height (m)

H d :

dispersion height (m)

H L :

gas-free liquid height (m)

H R :

riser height (m)

I :

inhomogeneity (-)

K :

consistency index (Pa sn)

k L a :

volumetric gas-liquid oxygen mass transfer coefficient (s−1)

m :

exponent in Eq. (12) (-)

n :

flow behaviour index (-)

P G :

power input due to gassing (W)

t M :

mixing time (s)

V A :

connecting pipe volume (m3)

V D :

downcomer volume (m3)

V d :

volume of dispersion (m3)

V R :

riser volume (m3)

V T :

total reactor liquid volume (m3)

v SGR :

riser gas superficial velocity (m s−1)

ɛ GR :

riser gas holdup (-)

\(\dot \gamma \) :

shear rate (m s−1)

η app :

apparent viscosity (Pa s)

τ :

shear stress

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Authors and Affiliations

  1. Research Center for Antibiotics, Chemical-Pharmaceutical Research Institute, Valea Lupului no. 1, 6647, Iasi, Romania

    M. Gavrilescu

  2. Faculty of Industrial Chemistry, Department of Transfer Phenomena and Chemical Engineering, Technical University of Iasi, 6600, Iasi, Romania

    R. Z. Tudose

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  1. M. Gavrilescu
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  2. R. Z. Tudose
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Gavrilescu, M., Tudose, R.Z. Effects of downcomer-to-riser cross sectional area ratio on operation behaviour of external-loop airlift bioreactors. Bioprocess Engineering 15, 77–85 (1996). https://doi.org/10.1007/BF00372981

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