Countercurrent extraction with feed at intermediate stage

Find the minimum solvent flowrate for Example 5.2. Solution  

Since On+i = 1000 kg/hr, Vbmin = 1600 kg/hr. The actual solvent flowrate in the previous example was 2500 kg/hr, so Vo/ Vbmin = 1.6 for that extraction process. Using even more solvent would decrease the required number of equilibrium stages. 

8 Countercurrent extraction with feed at intermediate stage 

The concentration of solute (A) in the outlet extract stream is limited to a relatively low value because the outlet extract stream is a passing stream with feed On+i. So the maximum concentration of A in Vn will occur when the column is operated at the minimum solvent flowrate. As with distillation, this limitation can be overcome by using 

Extract reflux involves taking part of the exiting extract stream and changing it into a raffinate phase by removing solvent and returning this raffinate phase to the column. The solvent is usually removed by distillation, but can be removed by other 

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