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Separation Process Principles- 2n - Seader &amp; Henley - Solutions Manual

8 is positioned 80 of the vertical distance from the

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Unformatted text preview: d total condenser. Vapor-liquid equilibrium data. Assumptions: Constant molar overflow. Find: For a distillate of 95 mol% CS2 and a bottoms of 5 mol% CS2, determine: (a) Minimum reflux ratio, minimum boilup ratio, and minimum number of stages. (b) Number of trays. Analysis: (a) In the McCabe-Thiele plot on the next page, rectifying section and stripping section operating lines are shown for determining minimum reflux and boilup ratios. Note that the q-line has a slope given in Eq. (7-26) as q/(q - 1) = 0.5/(0.5 - 1) = -1 and intersects the point {0.4, 0.4}. The rectifying section operating line intersects the point {0.95, 0.95} and the point where the equilibrium curve and the q-line intersect. The slope of that line is measured to be L/V = 0.642. From Eq. (7-9), L/V = R/(R + 1). Rearranging, Rmin = (L/V)/[1 - (L/V)] = 0.642/(1 - 0.642) = 1.79 The stripping section operating line intersects the point {0.05, 0.05} and the point where the equilibrium curve and the q-line intersect. The slope of that line is measured to be L / V = 2.043. From Eq. (7-14), L / V = (VB + 1)/VB. Rearranging, V 1 1 = = = 0.959 (VB )min = B min ( L / V ) − 1 2.043 − 1 The McCabe-Thiele plot for minimum stages at total reflux is also shown on the next page. The operating lines are coincident with the 45o line. It is seen that 6 equilibrium stages are needed. (b) For a reflux ratio, R = L/D, of 4, the slope of the rectifying section operating line from Eq. (7-9) is L/V = R/(R + 1) = 4/5 = 0.8. This line and the stripping section operating line are shown on the third McCabe-Thiele diagram below. Except for the reboiler stage, the stages are stepped off from an efficiency line, which for a Murphree vapor efficiency of 0.8 is positioned 80% of the vertical distance from the operating line to the equilibrium curve, as governed by Eq. (7-41), EMV = 0.8 = (yn - yn+1)/(yn* - yn+1), where yn+1 is the location on the operating line, yn is the location on the efficiency line, and yn* is the location on the equilibrium line. However, the reboiler is assumed to have a 100% efficiency. As seen in the plot, just over 9 trays are required plus the partial reboiler. Call it 10 trays plus the reboiler. The feed plate is 7 from the top. Analysis: (a) (continued) Exercise 7.27 (continued) Analysis: (a) (continued) Exercise 7.27 (continued) Analysis: (b) (continued) Exercise 7.27 (continued) Exercise 7.28 Subject: Preliminary design calculations for the distillation of a benzene-toluene mixture. Given: Bubble-point feed of 50 mol% benzene and 50 mol% toluene. Equipment to include a partial reboiler, total condenser, and a bubble-cap tray column with an overall plate efficiency of 65%. Column to operate at 1 atm to produce a distillate of 95 mol% benzene and a bottoms of 95 mol% toluene. Vapor-liquid equilibrium data from Exercise 7.13. Enthalpy data for reboiler. Assumptions: Constant molar overflow and saturated liquid reflux. Find: (a) (b) (c) (d) (e) (f) Minimum reflux ratio (infinite s...
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