Distillation Column with an Intermediate Reboiler

Consider an ideal binary mixture with a constant relative volatility 2.85. This mixture is to be separated with a distillation column. The feed is a saturated liquid with 0.50 mole fraction of A (the light component). The feed, bottom, and distillate flow rates are equal to 20, 10, and 10, respectively (all expressed in kmol/hr). The reflux ratio is set equal to 2.25. The distillate and bottom specifications are 0.90 and 0.10 mole fraction of A, respectively. This column has an intermediate reboiler, whose flow rate and position can be set by the user (i.e., either one or two stages below the optimum feed location). No stages are stepped on the magenta line. Indeed, this corresponds to a situation where the vapor from the intermediate reboiler is input immediately below the stage where the liquid is withdrawn. This Demonstration shows the corresponding McCabe and Thiele graphical construction. The equilibrium curve is drawn in red. The feed line is 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 by a straightforward inspection of the graphical construction where and are the liquid and vapor mole fractions of component A.



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P. C. Wankat, Equilibrium Staged Separations, Englewood Cliffs, NJ: Prentice Hall, 1988.
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