Distillation Column with Liquid Side Stream
Consider an ideal binary mixture with a constant relative volatility equal to 2.85. This mixture is to be separated with a distillation column. The feed is a saturated liquid with 0.35 mole fraction of A (the light component). The feed, bottom, and distillate flow rates are equal to 45, 35, and 10, respectively (all expressed in kmol/hr). The reflux ratio is set equal to 2.25. The distillate specification is 0.90 mole fraction of A. This column has a liquid side stream, whose flow rate and position can be set by the user. The Demonstration shows the corresponding McCabe and Thiele graphical construction. The equilibrium curve is drawn in red. The feed line and the line corresponding to the liquid withdrawal are shown in cyan. The operating line for the three sections of the column (i.e., the top, middle, and bottom sections) are displayed in green. One can easily determine the total number of theoretical stages, the optimum feed stage location, and the composition of the liquid side stream by a straightforward inspection of the graphical construction where and are the mole fractions of component A.
P. C. Wankat, Equilibrium Staged Separations, Englewood Cliffs, NJ: Prentice Hall, 1988.