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

Separation Process Principles 2n Seader& Henley Solutions Manual

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Unformatted text preview: calculations. (a) Assume a pressure at the top of 314 psia, with 316 psia at the bottom and 315 psia at the feed location. Using the Flash model, run a bubble-point temperature calculation of the assumed distillate in lbmol/h of 26 C1, 9 C2, 24.6 C3, and 0.3 nC4 at 314 psia for both 0% (total condenser case) and 100% vaporized (partial condenser case). For a total condenser, the distillate temperature is found to be -100oF, which is infeasible. For a partial condenser, the distillate temperature is 73.1oF, which is possible, but very close to the cooling water temperature of 65oF. A bubble point calculation on the assumed bottoms in lbmol/h of 0.4 C3, 16.7 nC4, 11 nC5, and 12 nC6, at 316 psia is 301.9oF. The saturation temperature of steam at 315 psia is 421oF. Therefore, the steam is adequate, but may have to be throttled to a lower pressure to avoid film boiling in the reboiler. (b) When the feed is flashed at 315 psia to 66 mol% vapor, the temperature = 183.3oF. The computed K-values and relative volatilities (relative to the HK, nC4) are: Component K-value α referred to nC4 Methane 9.250 15.29 Ethane 3.081 5.09 Propane, LK 1.405 2.32 n-Butane, HK 0.605 1.00 n-Pentane 0.274 0.453 n-Hexane 0.126 0.208 Analysis (continued) Exercise 10.30 (continued) (c) The recovery of the LK, C3, to the distillate = 24.6/25 = 0.984. The recovery of the HK, nC4, to the distillate = 0.3/17 = 0.01765. Using the Shortcut (FUG) model of Chemcad, the following results are obtained: Minimum equilibrium stages = 10.5 Minimum reflux ratio = 0.87 Actual reflux ratio for 1.3 times minimum = 1.131 Number of equilibrium stages = 23.5 Feed stage from top = 11.5 Therefore, use, say, 10 theoretical plates in rectifying section plus a partial condenser, and 12 theoretical plates in the stripping section plus a partial reboiler. (d) For the rigorous TOWER model of chemcad, first use the following specifications for the case of a reflux ratio = 1.3 times minimum: Partial condenser Top pressure = 314 psia No condenser pressure drop. Column pressure drop = 2 psi Therefore, bottom pressure = 316 psia Number of stages = 24 (includes partial condenser and partial reboiler) Feed stage = 12 from the top At the top, reflux ratio = 1.131 At the bottom, bottoms flow rate = 40.1 lbmol/h Estimated distillate rate = 59.9 lbmol/h (actual rate) Estimated reflux rate = 59.9(1.131) = 67.75 lbmol/h (actual rate) Estimated temperature of stage 1 = 73oF Estimated temperature of bottom stage = 302oF Estimated temperature of stage 2 = 83oF The TOWER model converged in 4 iterations, with the following results, including the temperatures and concentrations at each stage, as requested in Part (e): Condenser duty = 417,600 Btu/h Reboiler duty = 482,500 Btu/h Top temperature = 72.9oF compared to assumed value of 73oF Bottom temperature = 302oF compared to assumed value of 302oF Stage 2 temperature = 105.2oF compared to assumed value of 83oF Note that the desired split of the two key components is achieved with: 0.2747 lbmol/h of nC4 (HK) in the distillate compared to a specification of 0.3 lbmol/h 0.3747 lbmol/h of C3 (LK)...
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This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.

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