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

0001 lbmol since 12 lbmol of holdup the plate column

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Unformatted text preview: n Eqs. (1) and (2) are solved simultaneously, the results are Rmin = 1.058 and Nmin = 2.668. Using the latter value in Eq. (13-27), . 01004 x DC = = 0.0244 2 .668 2 .668 0.3989 2 + 0.5007 15 . + 01004(1) 2.668 . From Eq. (13-25), 0.0244 2.668 0.0244 x DA = 0.3989 2 = 0.6164 and x DB = 0.5007 152.668 = 0.3592 . 0.1004 01004 . Exercise 13.25 (continued) Analysis: The calculations above for the first time increment are repeated for subsequent time increments, using a spread sheet, up to 1 hour. The results are as follows. Exercise 13.26 Subject: Calculation of batch rectification of a ternary mixture by a method that accounts for holdup. Given: Charge of 100 lbmol of 35 mol% n-hexane (C6), 35 mol% n-heptane (C7), and 30 mol% n-octane (C8). Batch rectification at 1 atm. Column with the equivalent of 10 theoretical stages, plus a partial reboiler and a total condenser. Constant reflux ratio, R = 5 and vapor boilup rate, V = 50 lbmol/h. Total reflux condition is established by time zero. Ideal thermodynamics (Raoult's law K-values). Holdup of condenser-reflux drum = 1 lbmol. Three operation steps: Step 1. Stop when accumulated distillate purity drops to 95 mol% C6. Step 2. Empty the C6-rich cut and resume rectification until instantaneous distillate composition drops reaches 80 mol% C7. Step 3. Empty the C6-rich cut and resume rectification until accumulated distillate composition reaches 4 mol% C8. Assumptions: No pressure drop. Find: Compositions and amounts of each of the 4 products for: Column 1: Plate column with a total liquid holdup of 8 lbmol. Column 2: Packed column with a total liquid holdup of 2 lbmol. Effect of holdup for the two columns. Analysis: Use the Batch distillation program of Chemcad to make the calculations. The flowsheet below includes a batch column (1), a time switch (2), and 3 tanks (3, 4, and 5). Exercise 13.26 (continued) Analysis (continued): To determine the effect of holdup, make a run with no holdup in the column or the condenser-reflux drum. For all three runs, the initial charge is first brought to the bubble point temperature, which is computed to be 193.2oF at 1 atm. Case 1: Column and condenser-reflux drup with no holdup: The input data for Chemcad are as follows, where distillate rate = D = V/(1+R) = 50/6 = 8.333 lbmol/h. Batch column: No. of stages = 12 (10 in column + reboiler + condenser) No. of operation steps = 3 Total condenser Condenser pressure = 1 atm Holdup units in moles (lbmoles in this case) Condenser holdup = 0 Stage holdup = 0 Method of calculation = Inside-out Operation parameters: Step 1 2 3 Startup option Total reflux Column content Column content Tank no. 3 4 5 First specification Reflux ratio = 5 Reflux ratio = 5 Reflux ratio = 5 Second specification Distillate rate = 8.333 Distillate rate = 8.333 Distillate rate = 8.333 lbmol/h lbmol/h lbmol/h Step size, hr 0.02 0.02 0.02 Record frequency 3 3 3 Stop criterion Mole fraction of C6 in Mole fraction of C7 in Mole fraction of C8 in accumulator = 0.95 inst...
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This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.

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