Figure 12.13b Distribution coefficient
as a function of the maximum substrate
conversion for which a three-phase
fluidised bed performs equally well as
a liquid fluidised bed. Uc=1.29 cm/s,
=100 mol/m
3, Ud=0.14 cm/s,
Ud=0.55 cm/s Ud=0.91 cm/s
X vmax (mol/m^3 s) t
batch (99%) (min) =100 mol/m
(^3) mol/m (^3)
0.001 20950
0.01 2108
0.05 435.5
0.1 227.9
1 32.3
At the lower water fluxes, Figure 12.13a and Figure 12.13b, the decrease in gel-bead
hold-up is not that large, less than 15% for all dodecane fluxes applied, and there is
hardly any difference in gel-bead hold-up between the highest and lowest dodecane flux.
Thus, the transfer rate in the three-phase fluidised beds, necessary to perform equally
well as the two-phase fluidised bed, are more or less the same. So, at these water fluxes, a
higher distribution coefficient is needed for the lower dodecane flux to establish a high
enough transfer rate.
For the highest water flux applied, Figure 12.13c, there is a significant decrease in
gelbead hold-up with an increasing dodecane flux (compared to the two-phase fluidised-
bed analogue, 39% for the highest dodecane flux and 7% for the lowest). Consequently,
the transfer rate must be higher for the higher dodecane fluxes. When a lower distribution
coefficient is used for the higher dodecane fluxes, as above for the lower water fluxes, the
resulting transfer rate is not enough for establishing the required transfer rate, although
Design of liquid-liquid-solid fluidised-bed bioreactors 375