CPB 20103 Mass Transfer 2

FG/T3/July2011

CPB 20103 MASS TRANSFER 2 TUTORIAL 3

CRYSTALLIZATION OPERATIONS

1. A hot solution of FeSO4 from an evaporator contains 30.6 kg FeSO4/100

kg H2O and goes to a crystallizer where the solution is cooled and FeSO4 crystallizes. On cooling, 10% of the original water present evaporates. For the feed solution of 100 kg total, calculate the following:

a) The yield of FeSO4.7H2O crystals if the solution is cooled to 290 K where the solubility is 8.6 kg FeSO4/100 kg H2O.

b) The yield of FeSO4.7H2O crystals if the solution is cooled instead to 283 K where the solubility is 7.0 kg FeSO4/100 kg H2O.

2. A hot solution containing 1000 kg of MgSO4 and water having a

concentration of 30 wt% MgSO4 is cooled to 288.8 K where crystals of MgSO4.7H2O are precipitate. The solubility at 288.8 K is 24.5 wt% anhydrous MgSO4 in the solution. Calculate the yield of crystals obtained

a) if 5% of the original water in the system is evaporates on cooling. b) if 5% of the total weight of solution is evaporates on cooling.

3. Feed to a cooling crystallizer is 1000 lb/hr of 32.5 wt% MgSO4 in water at 120oF. This solution is cooled to 70oF to form crystals of heptahydrate. Estimate the heat of removal rate in Btu/hr. Given the specific heat of solution is 0.72 Btu/lb.oF and the heat of solution is 23.2 Btu/lb of heptahydrate.

4. A solution consisting of 30% MgSO4 and 70% H2O is cooled to 60oC.

During cooling, 5% of the total water in the system evaporates. Calculate the amount of crystals obtained per 1000 kg of original mixture.

5. Copper sulfate is crystallized as CuSO4.5H2O by combined

evaporative/cooling crystallization. 1000 kg/hr of water is mixed with 280 kg/hr of anhydrous copper sulfate at 40oC. The solution is cooled to 10oC and 38 kg/hr of water is evaporated in the process. Calculate the amount of crystals can be collected theoretically.

6. A batch of 1000 kg of KCl is dissolved in sufficient water to make a

saturated solution at 363 K where the solubility is 35 wt% KCl in water. The solution is cooled to 293 K at which temperature its solubility is 25.4 wt%.

a) Calculate the weight of water required for solution b) Calculate the weight of crystals obtained if 3% of the original

water evaporates on cooling.

7. Determine the effect of crystal diameter on the solubility of KCl in water at 25oC. Given: Molecular weight of KCl = 74.6 Density of KCl = 1980 kg/m3

Ahmad Muzammil Bin Idris

CPB 20103 Mass Transfer 2

FG/T3/July2011

Average interfacial tension = 0.028 J/m2

8. Using the data in Question (4), estimate the effects of supersaturation ratio, on the primary homogeneous nucleation of KCl from an aqueous solution at 25oC for values of of 2.0, 1.5 and 1.1.

9. Determine the supersaturation ratio required to permit 0.5m diameter

crystals of sucrose to grow if average interfacial tension is 0.01 J/m2. Given: Molecular weight = 342 Density = 1590 kg/m3

10. If the desired production rate in the crystallizer is 4200 kg/hr of MgSO4.7H2O, the volume of liquid in the crystallizer is 7.7 m3 and the nucleation rate is 2.7 x 109 nuclei/m3.hr, estimate the predominant crystal size. What would it be if the nucleation rate were 2.0 x 108 nuclei/m3.hr? (assume a = 1)

CPB 20103 Mass Transfer 2

FG/T3/July2011

Molecular weights: MgSO4 = 120.38 MgSO4.7H2O = 246.49 Molecular weights: FeSO4 = 151.8 FeSO4.7H2O = 277.8 Molecular weight: CuSO4 = 160 CuSO4.5 H2O = 250