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

53 lbmolh actual rate estimated 2nd draw rate 2478

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Unformatted text preview: 5.00 0.00 14.71 0.29 23.42 1.58 3.71 16.29 2.06 32.94 48.90 51.10 The example in Perry's Handbook is for a column with a total condenser, while this exercise calls for a partial condenser. Thus, this exercise has 11 instead of 10 equilibrium stages. Nevertheless, the solution from Perry's Handbook shows a slightly sharper separation. This is probably due to the differences in K-values. For example at a mid-column temperature of 210oF, the Grayson-Streed correlation predicts a relative volatility between n-butane and isopentane of 1.82, while the graphical correlation used in Perry's Handbook predicts a higher value of 1.94. Subject: Exercise 10.26 Distillation of an light alcohol mixture using UNIFAC equation. Given: Feed of 1000 kmol/h of a bubble-point mixture of 60 mol% methanol (M), 20 mol% ethanol (E), and 20 mol% n-propanol (P) is sent to the middle stage of a column with a total condenser, 3 equilibrium stages in the column, and a partial reboiler, and operating at 1 atm. The distillate rate = 600 kmol/h and the reflux rate = 2,000 kmol/h. Find: Product compositions, stage temperatures and vapor and liquid traffic, reboiler and condenser duties, and stage compositions for converged solution. Analysis: The calculations were made with the TOWER model (Inside-out method) of the Chemcad program, with the following specifications: Total condenser Top pressure = 1 atm No condenser or stage pressure drop. Therefore, bottom pressure also = 1 atm Number of stages = 5 (includes total condenser and partial reboiler) Feed stage = 3 from the top At the top, reflux rate = 2,000 kmol/h At the bottom, bottoms rate = B = F - D = 1000 - 600 = 400 kmol/h Estimated distillate rate = 600 kmol/h (actual rate) Estimated reflux rate = 2000 kmol/h (actual rate) Estimated temperature of stage 1 = 30oC Estimated temperature of bottom stage = 100oC Estimated temperature of stage 2 = 40oC The feed is given as a bubble-point liquid at 1 atm. The UNIFAC equation gives a bubble-point temperature of 70.1oC. Based on the feed composition, the distillate rate of 600 kmol/h corresponds to a desired split between methanol and ethanol. The enthalpies were computed by the Latent Heat model with a correction for the heat of solution based on liquid-phase activity coefficients from the UNIFAC equation. The calculations converged in 8 outer-loop iterations with results given below and on the following pages. Condenser duty = 93,592 MJ/h Reboiler duty = 93,841 MJ/h Top temperature = 70.1oC compared to assumed value of 30oC Bottom temperature = 79.2oC compared to assumed value of 100oC Stage 2 temperature = 67.3oC compared to assumed value of 40oC Exercise 10.26 (continued) Analysis: (continued) Exercise 10.26 (continued) Analysis: (continued) Exercise 10.27 Subject: Distillation of a 4-component mixture with two sidestreams in an attempt to obtain four nearly pure products. Given: Feed of composition given below at 150oF and 25 psia. Column pressure of 20 psia at top and 25 psia at the bottom Column has a total condenser giving saturate...
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