Constraints ◾  49
When the stripping factor is infinite, the number of mass
transfer units can be calculated by Equation 6.4:
N OL = Ln(x F /x B )
(6.4)
When the stripping factor is equal to 1.0, the values of NTS
and N OL are identical (Equation 6.5).
For S = 1.0:
N OL = NTS = x F /x B – 1
(6.5)
In other words, reducing a light solute in the liquid from 1,000
ppm to 1 ppm requires 999 theoretical stages or mass transfer units when the stripping factor is 1.0. Table 6.1 shows a
comparison of the number of theoretical stages and the number of liquid transfer units required for reducing the solute
Table 6.1 Number of Theoretical
Stages and Liquid Mass Transfer
Units for Stripping 1000 ppm Light
Impurity down to 1 ppm
S
NTS
N OL
1.0
999.00
999.00
1.1
47.42
49.72
1.2
28.09
30.73
1.3
20.75
23.59
1.5
14.33
17.43
2.0
8.97
12.43
5.0
4.15
8.36
10.0
2.95
7.56
20.0
2.29
7.22
100.0
1.50
6.97
∞
0.00
6.91