Page 162 - Adsorption, Ion Exchange & Catalysis- 2007, Elsevier - Copy

Else_AIEC-INGLE_cH003.qxd 7/13/2006 1:45 PM Page 158
158 3. Heterogeneous Processes and Reactor Analysis

0.55
Spheres
Cylinders
0.5

0.45
bed voidage
0.4

0.35
0 0.1 0.2 0.3 0.4
/D
d p
Figure 3.39 ersus Bed voidage v d / D .
p

A well-known method is the “snow-storm filling, as shown in Figure 3.40
”
oumen
,
y
v
olv
(Afandizadeh and F 2001). This method ines passing the packing material
over staggered wires or wire meshes so that the fall of the particles is interrupted before
reaching the bed fThe flow interruption causes radial dispersion of particles, and as a ace.
consequence, the entire bed face is coered at a uniform rate. v
Liquid flow distribution in fixed beds
General Generally, from a macroscopic point of view, maldistribution can be divided into
irst one is small-scale maldistibution, The f two different phenomena (Stanek, 1994). which
is connected mainly to the so-called preferred paths. It is the case where the
liquid follows specific paths through bed and traels with velocities considerably higher v
than the mean. The same phenomenon is characterized as chaneling. The second case is
large-scale maldistribution, which is connected to the nonhomogeneous (nonuniform) ini-
tial distribution of the liquid and is referred to as “wall effects.” The concepts of distributor
quality and liquid maldistribution in fixed beds are frequently found in the related technical
literature, and these concepts are connected to each other—the better the distrib utor qual-
ity, the better the liquid distrib 1995). w into bed (Klemas and Bonilla, ution and flo
The distributor quality D Q , is expressed as the portion (%) of the fed-bed cross- ix
sectional area (inlet surf which is homogeneously wetted by the liquid. The initial
ace),
maldistribution in the bed inlet ( M do ) is a statistical average of the mass flow rate standard
deviation divided by the free surface in the bed inlet. These parameters are related as fol-
lows (Klemas and Bonilla, 1995):

M 100 (100 ) D D 0.5 (3.337)
do Q Q
For example, for a distributor quality of 90–95%, the initial maldistrib ution is 23–33%.
This means that the distributor should have excellent quality to lead to a good initial liquid