Question

10 000 kg/hr of a 5% salt in water solution is fed to a desalination unit where the salt is removed from the water to produce fresh water and brine. The desalinated water is to contain no more than 500 ppm salt. The brine (salt solution) waste from the process contains 7.25% salt. To optimize the process, some of the brine waste is recycled to the process. After mixing the process input contains 6% salt. 6.1 Draw a flow diagram of the process. (8) 6.2 Calculate the flowrates of the brine, desalinated water and recycle streams. (10)

Answer 1

Page No Fresh Feede Mixed © Feed F = 10000 Meglho CM) ) water Desalinated Desalination Unit Salt - 5. TS Salt - 64 salt - 500 ppm HO 951- waste Brine (W) Salt - 7.25 7. Reeyue CRD Salt - 7.25.1. Prine (B) Salt - 7.25". → Overall Conside Point ② Mass Balaru at - F + R . 10000 + B 2 is given as - Point = - M M Salt Mass Balance at Point ® is given as 00 " : 0.05 x 10000 0.06M - + 0.0725 R 0.0725 R M = = 0.06 500 - ③ 2 Solving equations IR = 8000 M = 18000 and uglhr Kglhr

Page No. 1- To convert ppm to wtt muutiply by 10' = 500 x 10-4 = 0.05 wt oL i wt% of salt in Stream D wt t. OLUS Consider Unit :- overall Mass Balance on Unit M = D + w : 18000 - D+ w → Salt Mass Balance on unit gives (6) M = (0.os) 0 + (1.25) w 0.06 x 18000 = 0.0005 +0.0725 w → ① 1 solving ④ P W equations = 3125 : 14875 3 and Ka Loc Malhe Consider On Point ① overall Mass Balance w = B +R B = W-R = B = 6875 kg/hr L : 14875 - 8000 Brine out Brine out Desalinated Recycle of of water wnit process = = w B D R = = = = 14875 neglhr 6875 ughhr 3125 U hr 8000 kglur =