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

13 continued analysis continued eq 8 shows that the

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Unformatted text preview: the partial reboiler) Feed stage = 12 from the top Reflux ratio = 2 Bottoms mole flow rate = 1200 lbmol/h Estimated distillate rate = 200 lbmol/h Estimated reflux rate = 400 lbmol/h Estimated temperatures: Stage 1, 200oF Stage 16, 300oF Stage 2, 220oF A converged result, which showed a slightly better separation than specified for the FUG method, was obtained in 17 iterations: However, as shown in the composition profile on the next page, a pinch region (where no composition changes occur) of approximately 3 stages is evident just above the feed stage. Accordingly, the calculations with the Tower model were repeated by removing 3 stages above the feed, resulting in the following new input: Number of stages = 13 (includes the total condenser and the partial reboiler) Feed stage = 9 Exercise 11.12 (continued) Analysis: Ordinary Distillation Column (continued) A converged result was obtained in 17 iterations, with little change in the separation. The composition profile for this run appears on the next page. No pinch is evident. The ordinary distillation column for separating methanol from ethanol was sized with Chemcad for sieve trays, with: 24-inch tray spacing 12% downcomer area 10% hole area 1/4-inch holes 80% of flooding The resulting column inside diameter was determined to be 5.5 feet. The condenser duty was computed to be 8.53 million Btu/h, with a reboiler duty of 11.70 million Btu/h. For a final design, the computations should be repeated taking into account tray pressure drop and tray efficiency. The final material balance for the ordinary distillation column was as follows: Component n-Heptane Toluene Phenol Total: Temp., oF lbmol/h: Feed Distillate 1.8 1.8 198.8 197.0 1199.4 1.2 1400.0 200.0 323.3 251.0 Bottoms 0.00 1.8 1198.2 1200.0 378.2 Because the flow rate of phenol in the bottoms is only 1198.2 lbmol/h and 1200.0 is needed for the extractive distillation column, the makeup phenol rate is 1200.0 - 1198.2 = 1.8 lbmol/h. Exercise 11.12 (continued) Analysis: Ordinary Distillation Column (continued) Exercise 11.12 (continued) Analysis: Ordinary Distillation Column (continued) Exercise 11.13 Subject: Separation of a mixture of ethanol and benzene by pressure-swing distillation. Given: Feed of 100 mol/s of 55 mol% ethanol and 45 mol% benzene at the bubble point at 101.3 kPa. Desired products are 99 mol% ethanol and 99 mol% benzene. Assumptions: UNIFAC method for estimating K-values. Find: Feasible design using pressure-swing distillation in the manner of Example 11.5 and Fig. 11.23(b). Analysis: Use the two-column system of Fig. 11.23(b). Ethanol and benzene form a minimumboiling azeotrope. Use the same column pressures as in Example 11.5. Therefore, in Column 1, the pressures are 26 kPa at the condenser outlet, 30 kPa at the top tray, and 40 kPa at the reboiler. The distillate product is the near azeotrope at 30 kPa and the bottoms product is 99 mol% ethanol. In Column 2, the pressures are 106kPa before the condenser, 101.3 kPa after the condenser, and 120...
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