Multiphase Bioreactor Design

Hydrodynamics

This part of the model considers the hold-up and mixing of the different phases present.
To model the medium flow, the fluidised bed is divided in a number of ideally mixed
tanks. For a fluidised bed of 1 m high, and for medium fluxes between 0.5×10−^2 and 2×
10 −^2 m/s, the number of tanks has been experimentally determined. It appears that for
medium fluxes the number of ideally mixed tanks is equal to 13 for the two-phase
fluidised bed and 3 for the three-phase fluidised bed.
In order to make the reactor model less complicated, it is assumed that gel beads
remain in one tank and do not circulate between the different tanks.
A model has been developed for predicting the hold-ups in a three-phase fluidised bed
(van Zessen, 2000), but we chose to use the experimentally determined hold-ups as they
are more accurate. The dodecane hold-up and gel bead hold-up as a function of medium
flux and dodecane flux is shown in Figure 12.6.

Figure 12.6 a: droplet hold-up as a

function of the water and dodecane

flux. Ud=0.05cm/s, Ud=0.10 cm/s,

Ud=0.18cm/s,  Ud=0.27 cm/s,

Ud=0.44cm/s, Ud=0.54 cm/s,

Ud=0.73 cm/s, ×Ud=0.91 cm/s b: Gel

bead hold-up as a function of the water

and dodecane flux. Uc=0 cm/s,

Uc=0.10 cm/s, Uc=0.29 cm/s,

Uc=0.42 cm/s,  Uc=0.54 cm/s,

Uc=0.75 cm/s, Uc=0.91 cm/s

Table 12.1 gives an overview of the assumptions made and the models used for
determining the hold-up and mixing characteristics of both reactors.

Mass transfer

Multiphase bioreactor design 362