Page 224 - Adsorption, Ion Exchange & Catalysis- 2007, Elsevier - Copy

Else_AIEC-INGLE_cH003.qxd 7/13/2006 1:46 PM Page 220
220 3. Heterogeneous Processes and Reactor Analysis

As in the case of two-phase fed beds and trickle beds, the material balances of fluidized ix
beds are written in terms of reactor v olume ( V R ation) and the ) (see Section 3.1.1 for deri v
following relationship holds:

1d N V V
( R ) S ( r vs ) L ( r ) u (3.521)
V d t V V
R R R
For the bubble phase,

V
L
(3.522)
V bub
R
V S V bubble V S
(3.523)
V V V bub b
R R bubble
Then, the oerall rate of reaction ( v –R ) per unit volume of reactor is

1d N
( R ) bub b ( r ) u ( r ) (3.524)
bub
vs
V d t
R
For the emulsion phase,
V L V emulsion V L

(1 ) (3.525)
V V V bub fm
R R emulsion
V S V emulsion V S
(1 )(1 ) (3.526)
V V V bub fm
R R emulsion

Then, the oerall rate of reaction (– v R ) per unit volume of reactor is
1d N
( R ) (1 bub )(1 )( ) r ) ) u (3.527)
(1
r
(
bub
vs
fm
fm
V d t
R
Kunii-Levenspiel three-phase model (bubbling bed model)
wing,
In the follo a simplified version of the Kenspiel model is presented
unii–Le
v
(Levenspiel, 1962). This design model follows the assumptions of the bubbling bed one.
According to this hydrodynamic model, the solids in the emulsion phase flow smoothly
downward (plug-flow of solids). The entire emulsion phase is thoroughly agitated,
whereas the emulsion exists at minimum fluidizing conditions. The gas occupies the same
void fraction in this phase as it would in the entire bed at minimum fluidization.
v
xists,
Furthermore, the reaction takes place whereer the solid e i.e. in the b in the ubbles,
wakes, and in the emulsion phase. In Figure 3.64, the model is schematically presented.