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3.4 Slurry Reactors 115

eactor Flow regimes in slurry bubble column r s
The hydrodynamics of bubble columns and slurry bubble column reactors depend strongly
on the flow regime (Figure 3.27). There are three flow patterns that preail in these reac- v
tors (Wallis, 1969; Shah et al ., 1982):
• homogeneous regime or bubbly flow or quiescent b ubbling
• heterogeneous regime or churn-turbulent flo w
• slug-flow regime.

In the bubbly flow re there is a homogeneous distribution of small and almost
gime,
identical gas b generally in the range 1–7 mm (Krishna, 2000). The gas velocity is
ubbles,
usually less than 0.05 m/s and the interaction among gas bubbles is weak. Under these con-
ditions, the gas bubbles do not affect the liquid motion and almost no liquid mixing is
observed. The gas bubble formation in this regime depends strongly on the injection point
(Magaud et al ., 2001; Saraf i et al ., 1999).
As the gas velocity is increased, there is more interaction among gas bubbles and both coa-
ulent flo This is the churn-turb lescence and breakup of bw or the het- ubbles are observ ed.
erogeneous regime, where the larger gas bubbles (generally in the range 20–150 mm) move
in plug flow, creating liquid recirculation as well as backmixing (Shah et al ., 1982). The large

Figure 3.27 Flow regimes in slurry bubble reactors