Chapter 6, Problem 6.86P

Potassium dichromate (K₂Cr₂O₇) is to be recovered from a 21 wt% aqueous solution in a continuous crystallization operation. The solution is joined by a recycle stream and fed to a vacuum evaporator where water is removed and the remaining solution is cooled to 30°C, at which temperature the solubility of the salt is 0.20 kg K₂Cr₂O₇/kg H₂O. The solution and suspended potassium dichromate crystals ?ow to a centrifuge. The crystals and 5.0% of the solution constitute the solids recovered from the centrifuge, and the remaining solution is recycled to the evaporator. The solids, which contain 90 wt% crystals and 10% entrained solution, are fed to a dryer, where they are contacted with hot air. The remaining water in the solids is evaporated, leaving pure potassium dichromate crystals. The air leaves the dryer at 90°C and 1 atm with a dew point of 392°C. For a production rate of 1000 kg solid K₂Cr₂O₇/h, calculate the required feed rate (kg/h) of 21% solution, the rate of evaporation of water in the evaporator (kg/h), the ?ow rate (kg/h) of the recycle stream, and the feed rate of air (standard liters/h).