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

11 mol vaporized convergence of the calculations was

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: of Products 1 and 2. The computed dew-point pressure at 130oF = 6.7 psia. This is too low. Therefore, set top pressure to 20 psia with a partial condenser. Distillate temperature at this pressure = 190oF. Sequence 2, Column 2: Distillate is Product 1. Therefore, again set pressure to 118 psia with a partial condenser. Analysis: (continued) Exercise 10.32 (continued) Now, use the Shortcut model in Chemcad to estimate stage and reflux ratios using R = 1.3Rmin. Results are as follows, where recoveries are of the column feed to the distillate: Sequence 1 Sequence 1 Sequence 2 Sequence 2 Column 1 Column 2 Column 1 Column 2 Pressure, psia 118 20 20 118 Light key, LK Methane Benzene Benzene Methane Heavy key, HK Benzene Toluene Toluene Benzene Recovery of LK 0.9948 0.9870 0.9870 0.9948 Recovery of HK 0.00495 0.00118 0.00118 0.005012 Minimum stages 2.04 14.37 13.28 2.01 Min. reflux ratio 0.0685 1.188 0.930 5.628 Reflux ratio 0.0822 1.425 1.209 7.317 No. of stages 8.97 32.35 29.23 4.55 Feed stage from top 4.60 23.99 21.34 2.26 Now design the two sequences using the rigorous Tower model of Chemcad. For each column, the top specification is the flow rate of the LK in the distillate and the bottom specification is the flow rate of the HK in the bottoms. The stage specifications and estimated reflux and distillate rates are taken from the above shortcut results, with some modest changes. The rigorous Tower model then computes the required reflux ratio and distribution of nonkey components. The results are as follows, where the total stages includes the condenser (total or partial) and the reboiler. The feed stage is counted from the condenser as stage 1. Sequence 1 Sequence 1 Sequence 2 Sequence 2 Column 1 Column 2 Column 1 Column 2 Top pressure, psia 118 20 20 118 Pressure drop, psia 2 2 2 2 Total stages 3 30 30 5 Feed stage 2 22 21 2 Reflux ratio 2.2 1.363 1.101 0.0042 Condenser duty, Btu/h 892,100 8,122,800 4,074,800 1,900 Reboiler duty, Btu/h 4,227,300 6,135,800 8,843,100 2,748,100 T of bottoms, oF 347.4 258.8 258.8 404.6 Lbmol/h of toluene in Product 1 0.063 0.0002 Sequence 2 requires an expensive two-stage compression system to take the vapor distillate from Column 1 at 20 psia and increase its pressure to 119 psia to deliver it to Column 2. Note that Column 2 uses such a small amount of reflux, that it is essentially just a reboiled stripper. Sequence 1 is simpler and preferred over Sequence 2. However, the first column in Sequence 1 would benefit with more reflux and stages to reduce the loss of toluene. Exercise 10.33 Subject: Separation of propylene from propane by distillation using a rigorous equilibriumstage model Given: Feed of 360 lbmol/h of propylene and 240 lbmol/h of propane at 125.7oF and 294 psia. Distillate is to be 99 mol% propylene, and bottoms is to be 95 mol% propane. Column is equipped with a partial condenser and a partial reboiler. Pressure is 280 psia in the reflux drop. Condenser pressure drop is 2 psia, and tray pressure drop is 0.1 psi/tray. Tray efficiency is 10...
View Full Document

This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.

Ask a homework question - tutors are online