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342 4. Adsorption and Ion Exchange

Then

D 2 D 2 Z  D 3 Z 
V o Z   D  
4 4 D   4 D  

To aoid large-scale liquid maldistrib the aspect ratio ution, Z/ D should be greater than 5
v
(see eq. (3.324)). If we choose the value of 10, then

V 4  D    1/3
D  o    0.234 m
 Z   

and thus Z 2.34 m. At the same time,

D
117 30
d p

Z
1168 150
d p

Thus, for the selected D and Z , large-scale maldistribution is preented (see eq. (3.324)). v
Relative flow rate limits : According to Ruthven (1984), a maximum linear v elocity
should not be exceeded in order to aoid extended friction between the packing material v
w operations. in both down- and upfloThis velocity is 0.8 times the minimum fluidization
velocity for upflow operation and 1.8 times the same velocity for downflow operation (for
further analysis see Chapter 6). Using eq. (3.451), the minimum fluidization velocity for
the specific system is 2.36 cm/s. Thus, the maximum alloable velocities for down- and w
upflow operations are 4.24 and 1.89 cm/s, respecti. In terms of the relatie flow rate, ely v v
the corresponding values are 65.35 and 29.13 BV/h. These values are fairly high for ion-
exchange systems and are rarely used in practical applications.
Apart from these “hydraulic” limits, one more limit comes from the model as analyzed
before. We found that

1
N (
1.2311
N T
min
or, by using eq. (4.139),
15 DV
s o 1.2311
rQ 2
o
The relative volumetric flow rate is (eq. (3.103))

V 1
o
Q Q rel