One hundred kmol/h of a saturated-liquid mixture of 12 mol% ethyl alcohol in water is distilled continuously using open steam at 1 atm introduced directly to the bottom plate. The distillate required is 85 mol% alcohol, representing 90% recovery of the alcohol in the feed. The reflux is saturated liquid with L/D = 3. Feed is on the optimal stage. Vapor–liquid equilibrium data are given in Exercise 7.29. Calculate: 

(a) The steam requirement in kmol/h; 

(b) The number of theoretical stages; 

(c) The optimal feed stage; and 

(d) The minimum reflux ratio, (L/D)min.

Data From Problem Exercise 7.29

A continuous distillation unit, consisting of a perforated-tray column  with a partial reboiler and a total condenser, is to be designed  to separate ethanol and water at 1 atm. The bubble-point feed contains  20 mol% alcohol. The distillate is to contain 85 mol% alcohol,  and the recovery is to be 97%. 

If the L/V is 0.80,  how many actual plates will be required?  Vapor–liquid equilibrium for ethanol–water at 1 atm in terms of  mole fractions of ethanol are [Ind. Eng. Chem., 24, 881 (1932)]:

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X 0.0190 0.0721 0.0966 0.1238 0.1661 0.2337 0.2608 y 0.1700 0.3891 0.4375 0.4704 0.5089 0.5445 0.5580 T, °C 95.50 89.00 86.70 85.30 84.10 X 0.3273 0.3965 0.5079 0.5198 0.5732 82.70 0.6763 82.30 0.7472 0.8943 y 0.5826 0.6122 0.6564 0.6599 0.6841 0.7385 0.7815 0.8943 T, °C 81.50 80.70 79.80 79.70 79.30 78.74 78.41 78.15