Page 185 - Adsorption Technology & Design, Elsevier (1998)

Design procedures 171

Time t (hrs)

No
Slope =
Co U

~
Depth ft
..'"
..."'
Intercept b
.o""
."
...'"
~176

:o -1 )
In(J
,f
b
k Co
Figure 6.10 Bed depth service time graph (adapted from Faust and Aly 1987).

The slope can be modified from the original value a to the new value a' to
take account of a change in velocity from u to u' as follows:
au
new slope = a ~ = --- (6.58)
U'
Equation (6.58) is valid for the new flow velocity because velocity has little
or no effect on the intercept of the BDST plot which is given by b, as follows:

intercept b = c0kl In (c~ -1 (6.59)
)
-
The assumption is made here that the kinetics of adsorption are not
influenced to any appreciable extent by conditions external to the adsor-
bent, that is the rate of adsorption is controlled solely by processes which
occur inside the adsorbent particles. If this assumption is valid then data
from small-scale experiments can be reliably scaled up to other flow rates
without running pilot tests in larger columns.