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Unformatted text preview: Open Steam Case: Exercise 7.35
Distillation of two feeds of mixtures of water and acetic acid at 1 atm. Given: Feed 1 is a bubble-point liquid of 100 kmol/h containing 75 mol% water. Feed 2 is 50 mol% vaporized of 100 kmol/h containing 50 mol% water. Unit consists of a plate column, total condenser, and partial reboiler. Distillate is to contain 98 mol% water. Bottoms is to contain 5 mol% water. Reflux ratio, L/D = R = 1.2 times minimum. Vapor-liquid equilibrium data. Assumptions: Constant molar overflow. Find: Optimal feed stage locations and number of equilibrium stages. Analysis: Water is the more volatile component. Compute flow rates of distillate and bottoms. Overall total material balance: F1 + F2 = 100 + 100 = 200 = D + B (1) Overall water balance: (0.75)(100) + 0.5(100) = 125 = xDD + xBB = 0.98D + 0.05B (2) Solving Eqs. (1) and (2), D = 123.66 kmol/h and B = 76.34 kmol/h. Assume the minimum reflux is controlled by the upper feed. This is verified in the McCabe-Thiele di...
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