Effects of downcomer-to-riser cross sectional area ratio on operation behaviour of external-loop airlift bioreactors |
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Authors: | M Gavrilescu R Z Tudose |
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Institution: | (1) Research Center for Antibiotics, Chemical-Pharmaceutical Research Institute, Valea Lupului no. 1, 6647 Iasi, Romania;(2) Faculty of Industrial Chemistry, Department of Transfer Phenomena and Chemical Engineering, Technical University of Iasi, 6600 Iasi, Romania |
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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 Pas
n
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.List of Symbols
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 s
n
)
-
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)
-
GR
riser gas holdup (-)
-
shear rate (m s–1)
-
app
apparent viscosity (Pa s)
-
shear stress |
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Keywords: | |
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