Distillation Column with Two Feeds
A distillation column with a total condenser and a partial reboiler is used to separate a nonideal mixture composed of ethanol and water. Feed 1, the lower feed, is saturated vapor (, where is the feed quality), which is 30 mole% ethanol. Feed 2, the upper feed, is a subcooled liquid, which is 40 mole% ethanol. One mole of vapor must condense inside the column to heat four moles of feed two to its boiling point (, where is the feed quality). The column specifications are a distillate with 72 mole% ethanol and a residue with 2 mole% ethanol. The column has a reflux ratio equal to 1.0 and operates at a pressure equal to 101.325 kPa. Both feed 1 and 2 are input at their optimum feed locations. The total number of stages, for various values of the flow rates of both feeds (to be set by the user), can be obtained using the McCabe and Thiele graphical construction. The green lines are the operating lines for the top, middle, and bottom sections of the column. The blue lines are the feed lines for each feed. The equilibirum curve is shown in magenta and the staircase construction is displayed in black.
P. C. Wankat, Equilibrium Staged Separations, Englewood Cliffs, NJ: Prentice Hall, 1988.