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3.8 T Fluid–Solid Fluidized Bed Reactors w o-Phase, 205

n=3
0.5
0.1
0.4 0.2
0.3 0.3
0.4
0.2
0.1
FC
0
0 0.5 1 1.5
-0.1
-0.2
-0.3
-0.4
ε t
Figure 3.56 Foscolo and Gilibaro criterion ( n = 3).

(c) If , the fluidization regime is
t1 fm
• particulate, in the re gion
f t2
• Type B fluidization, in the re gion
fm f t2
This is the case of A 0.2 (assuming 0.4).
fm
As can be shown for several combinations of A and n , in the cases (b) and (c), is typ-
t2
ically very high ( and the regime is practically particulate and of T 0.98), ype B fluidiza-
ely v, tion respecti for the whole region following the incipient fluidization condition. The
same holds for case (a), where in practice, reersion from Tubbling to particulate v ype A b
fluidization is rather rare and is expected only for high v alues of A , typically in the re gion
. of 0.4 and higher
The determination of the minimum bubbling condition is rather difficult because a trial-
and-error procedure is needed for the ealuation of v n and u and subsequently, the non-
ter
linear Foscolo and Gibilaro equation has to be solved. Furthermore, in order to find the
operating fluidization regime, is needed, which in turn means that the fluidization re gime
f
has to be knoTo aoid this situation, the resulting characteristic voidages should be
wn.
v
“transformed” into the corresponding characteristic v for e P elocities using, xample, v’ s vlo a
equation. Then, using the known operating superficial v elocity u , the operating fluidiza-
s
tion regime can be found.
Thus, the Foscolo–Gibilaro criterion is useful only when it is desirable to find the
expected regimes for a specified fluidization system.
The following criterion could also be used to find the expected fluidization regime for a
specified system. Experiments on particulate fluidization show that particle and fluid den-
sities and fluid viscosity are the most significant factors affecting fluidization beha . vior
On the basis of this, a dimensionless discrimination number D has been suggested to
n