Question

Crystallization and Recycle. It is desired to produce 1000 kg/h of Na,PO, 12H2O crystals from a feed solution containing 5.6 wt % Na,PO4 and traces of impurity. The original solution is first evaporated in an evaporator to a 35 wt% Na3PO solution and then cooled to 293 K in a crystallizer, where the hydrated crystals and a mother liquor solution are removed. One out of every 10 kg of mother liquor is discarded to waste to get rid of the impurities, and the remaining mother liquor is recycled to the evaporator. The solubility ofNa,PO4 at 293 K is 9.91 wt %. Calculate the kg/h of feed solution and kg/h of water evaporated.

Answer 1

ne -t The objective is to prodce 00lh of Na-s P0 5.6 ut 12H,0 crystals Prom a feed solution which contains NaPo and taces of impuri Oiginal Solution of NaPou 35 wt , it is evaporated in on evaporator and then cooled to 293 K Solubulity of Na POu ,41 t % at 293 k Notw, we caloulate the ka/h of vater eopoyate Initial Concentation of MaPo 0.35 Initial Concentration of water035 -0 35 0.53 Molecul mass of hydsada R- Moleculon mass of an 380 164 R .32 final Concerdabon looo kalh C-x(2.32-)

Sabstibute valua in above equation 1000 ~.2.32. xo.65 (0.53-x)C1-0) 2.32 x 0,3445-0.66 χ 1000 - 1000 | 1-2.32 χ+χ | 2.32 x о、3445-0-652. 1000-1320 χ 0,7992-0.65. χ 999, 20 0-1319, 35 χ 999200 319 35 There fore în this concentxation 5Wty of wab ey is evaporated and initial feed solution is 250 ha/h