Potassium dichromate (K 2 Cr 2 O 7 ) is to be recovered from a 21 wt% aqueous solution in
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 flow to a centrifuge. The crystals and 5.0% of the solution constitute the solid effluent from the centrifuge, and the remaining solution is recycled to the evaporator. The solid effluent, which contains 90 wt% crystals and 10% entrained solution, is fed to a dryer, where it is contacted with hot air. The remaining water in the effluent is evaporated, leaving pure potassium dichromate crystals. The air leaves the dryer at 90°C and 1 atm with a dew point of 39.2°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 flow rate (kg/b) of the recycle stream, and the feed rate of air (standard liters/h).
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