Extraction - Principles of Chemical Separations with Environmental Applications - page 148

Balances on each of the three components (Table 5.2) around the entire system
are in error by between 0.5 and 3.5 lbs. This is much worse than the cross-flow case
(Figure 5.28), probably because the results of subsequent stages depend on the results
of the previous stage (i.e., errors propagate).

O 2 O 1 O 0

x 1

x 2 (A), x 2 (I ), x 2 (W ) (A), x 1 (I), x 1 (W ) x 0 (A), x 0 (I), x 0 (W)

2 1

V 3 V 2 V 1

y 3 (A), y 3 (I), y 3 (W) y 2 (A), y 2 (I), y 2 (W) y 1 (A), y 1 (I), y 1 (W)

V 3 2 V 3 2

y 3 (A), y 3 (I), y 3 (W ) y 3 (A), y 3 (I), y 3 (W)

O 0 O 1 O 2

1 2

x 0 (A), x 0 (I), x 0 (W ) x 1 (A), x 1 (I), x 1 (W) x 2 (A), x 2 (I), x 2 (W)

V 1 V 2

y 1 (A), y 1 (I), y 1 (W ) y 2 (A), y 2 (I), y 2 (W)

Figure 5.26 Countercurrent ( top )vscross-flow ( bottom ), Example 5.6.

Table 5.2 Balances on each of the three components, Example 5.6.

Countercurrent Cross-flow

V 1 31.4 lb / hr 18.67 lb / hr

y 1 (A), y 1 (W), y 1 (I) 0.125, 0.040, 0.835 0.140, 0.055, 0.805

V 2 28.5 lb / hr 16.79 lb / hr

y 2 (A), y 2 (W), y 2 (I) 0.043, 0.020, 0.937 0.065, 0.025, 0.910

O 1 7.1 lb / hr 6.33 lb / hr

x 1 (A), x 1 (I), x 1 (W) 0.270, 0.690, 0.040 0.298, 0.670, 0.032

O 2 8.6 lb / hr 4.54 lb / hr

x 2 (A), x 2 (I), x 2 (W) 0.130, 0.850, 0.020 0.175, 0.800, 0.025

Note that the countercurrent system provides a higher product flowrate as well
as improved separation.