Kremser Equation Applications
1. 1200 kg/hr of a liquid mixture containing 20% solute, 80% diluent by weight is to be
treated in a multistage, countercurrent extraction system. Fresh solvent entering the last
stage contains 0.8% solute by weight. It was found that the same recovery of solute by
weight was attained if five stages were present using pure solvent rate which is 1.5 times
the minimum, and also 3 stages were present but using a solvent rate which is 2.2318
times the minimum. Assume that the solvent and diluent are immiscible and that the
equilibrium relation Y = KD X, where X is in kg solute/kg diluent and Y is in kg solute/kg
pure solvent. Determine:
a. The value of KD in the equilibrium equation (2.5)
b. The percent recovery of the solute attained (92.815 % recovery)
c. Fresh solvent rate requirement for the two cases, kg/hr
(Fresh solvent rate 5 stages = 545.971 kg/hr;
Fresh solvent rate 3 stages = 812.331 kg/hr)
d. Final extract and raffinate rates for the two cases, kg/hr
5 stages: Final extract rate = 768.727 kg/hr
Final Raffinate = 977.244 kg/hr
3 stages: Final extract rate = 1035.087 kg/hr
Final Raffinate = 977.244 kg/hr
2. A countercurrent multiple stage contact extraction system is to treat 50 tons/hr of wet
sliced sugar beets, with fresh water as solvent. The beets have the following analysis:
component
water
pulp
sugar
mass fraction
0.48
0.40
0.12
The strong solution leaving the system is to contain 0.15 mass fraction of sugar and 97%
percent of the sugar in the sliced beets is to be recovered. Determine the number of
extraction cells required if each ton of dry pulp retains 650 kg/hr of pure solvent,
assuming equilibrium between the underflow and the overflow from each cell.
Number of extraction cells = 15.492 or 16
3. Same as number 2 but instead of constant solvent, each ton of dry pulp retains 3 tons of
solution.
Number of ideal stages = 4.783 or 5