Question

15 total points. a) 10 points. A large facility requires a demineralizer to produce makeup water for an industrial boiler. (Typically 50-90% of the condensate from the steam is returned.) Calculate the amounts of H2SO4 and NaOH (100% basis) required in a dual bed 7. ion exchange system supply to remove the calcium and chloride ions in 1000 m3 of water containing 125 mg CaCl2/L. Assume 100% efficiency of chemical usage (which is a good first assumption but is not correct). Use one mole of H2SO4 per mole of Ca, and one mole of NaOH per mole of CI. b) 5 points. How much acid and caustic (100% basis) are needed for this system to provide 2200 m/day. 8. 15 total points. a) 5 points. Calculate the osmotic pressure of a solution of 1,500 mg NaCl/L at 20°C, using Eqn. 6-4. Note: the osmotic coefficient is 0.95 b) 5 points. Assuming complete separation (which is not correct), calculate the concentration of NaCl in the reject stream of the first stage of this brackish water reverse osmosis membrane that has a 35% recovery. c) 5 points. Calculate the osmotic pressure of this solution at 320C.

Answer 1

7.a Design basis: 125 mg/l CaCl₂.

Total Volume to be treated = 1000m³ = 10⁶ litres

Total salt to be removed = 125mg/l x 10⁶ litres = 125 kg CaCl₂.

Molar Mass of CaCl2 = 40 + 35.5 x 2 = 111g

Total Cation moles required = 125000/111 = 1.126 kmol

Total Anion moles required = 125000/111 x 2 = 2.252 kmol

Hence, H₂SO₄ required = 1.126 x 98 kg = 110.348 kg

NaOH required = 2.252 x 40 = 90.08 kg

7.b For 2200 m³/day of water,

H₂SO₄ required = 110.348 x 2.2 = 242.757 kg/day

NaOH required = 90.08 x 2.2 = 198.176 kg/day