Problem 1

A 35% solution of potassium dichromate is fed to a crystallizer-dryer system. The Fresh Feed is joined by a recycle stream before entering the crystallizer where 1000 kg/h water evaporates, producing a 15% solution. The wet crop exiting the crystallizer contains potassium dichromate trihydrate along with 15% of the solution. The remaining solution comprises the recycle stream.

The wet crop, which contains 85% crystals, is Fed to a batch dryer. The air leaving the dryer is at 340 K and 1 atm and contains 19% oxygen. A portion of the outlet air is recycled and mixed with the dry air feed at a recycle ratio of 2. At the end of the operation, pure potassium dichromate crystals are produced.

a. Identify two aspects in the entire operation that makes it unrealistic and absurd.

b. Perform a DF analysis on the six (6) subsystems of this two-unit operation.

c. Determine the following:

• composition of the wet crop in %K2Cr2O7 and %H20

• fresh feed rate of the aqueous solution (kg/h)

• production rate of dry crystals (kg/h)

• recycle ratio at the crystallizer unit

• composition of the gross feed to the crystallizer

• dry basis composition of the gross feed to the dryer

• total product rate of wet air (SCFH)

Additional information:

• MW of KSCrSO7 [..] 294.18 g/mol

• MW of water [_] 18.02 g/mol

• Universal gas constant [.] 10.73 psi-ft3/lbmol-Rp