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

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Unformatted text preview: d liquid, a partial reboiler, and 28 equilibrium stages in the column with feed entering stage 14. Distillate rate = 14.08 lbmol/h and reflux ratio = 20. A liquid sidestream of 19.53 lbmol/h is withdrawn at stage 10 from the top, and a vapor sidestream of 24.78 lbmol/h is withdrawn at stage 24 from the top. Peng-Robinson equation of state for K-values and enthalpies. Find: Product compositions. Stage temperatures, vapor and liquid flow rates, and compositions. Reboiler and condenser duties. Analysis: The calculations were made with the TOWER model (Inside-out method) of the Chemcad program, with the following specifications: Total condenser Top pressure = 20 psia Total stage pressure drop = 5 psia. Therefore, bottom pressure = 25 psia Number of stages = 30 (includes total condenser and partial reboiler) Feed stage = 15 from the top Liquid sidestream from stage 11 from the top, at a flow rate of 19.53 lbmol/h Vapor sidestream from stage 25 from the top, at a flow rate of 24.78 lbmol/h At the top, reflux ratio = 20 At the bottom, bottoms rate = B = F - D - S1 - S2 = 98.33 - 14.08 - 19.53 - 24.78 = 39.94 lbmol/h Estimated distillate rate = 14.08 lbmol/h (actual rate) Estimated reflux rate = 280 lbmol/h (close to actual rate of 281.6 lbmol/h) Estimated temperature of stage 1 = 120oF Estimated temperature of bottom stage = 200oF Estimated temperature of stage 2 = 140oF Estimated 1st draw rate = 19.53 lbmol/h (actual rate) Estimated 2nd draw rate = 24.78 lbmol/h (actual rate) The feed condition at the specified temperature and pressure is computed to be just slightly greater than the bubble-point temperature. Based on the feed composition below, the distillate, sidestreams, and bottoms correspond to the flow rates of the four components in the feed. The calculations converged rapidly in 4 outer-loop iterations with results given below and on the following pages. Condenser duty = 2,834,600 Btu/h Reboiler duty = 3,493,700 Btu/h o Top temperature = 47.7 F compared to assumed value of 120oF Bottom temperature = 289.0oF compared to assumed value of 200oF Stage 2 temperature = 49.9oF compared to assumed value of 140oF Exercise 10.27 (continued) Analysis: (continued) A high reflux ratio is needed to minimize the effect of feed composition when attempting to obtain nearly pure sidestreams. Analysis: (continued) Exercise 10.27 (continued) Exercise 10.28 Subject: Distillation of a hydrocarbon mixture given in Exercise 10.25. Given: Bubble-point liquid feed of composition given below. Column has a partial condenser and a partial reboiler, with operation at 120 psia. Recovery of light key, n-butane, to distillate = 98%. Recovery of heavy key, isopentane, to bottoms = 98%. Grayson-Streed correlation for Kvalues and Redlich-Kwong equation of state for enthalpies. Find: Product compositions, reflux ratio, numbers of equilibrium stages above and below the feed, stage temperatures, interstage flow rates and compositions, reboiler duty, and condenser duty. Analysis: The calculations were made with the TOWER model (Inside-out method). Initially, it w...
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