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

Secondary oil at 80of and 400 psia of the composition

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Unformatted text preview: = 1,000 lbmol/h Estimated reflux rate = 1,000 lbmol/h Estimated temperature of stage 1 = 90oF Estimated temperature of bottom stage = 90oF Estimated temperature of stage 2 = 90oF Convergence was achieved only with great difficulty after 29 iterations. The problem was also solved with the SCDS Column model (simultaneous correction method) in only 8 iterations. The percent absorption of each component is as follows: Component Methane Ethane Propane n-Butane n-Pentane % Absorbed 4.8 21.0 60.6 97.3 99.95 The other results are presented on the next two pages. Exercise 10.37 (continued) Analysis: (continued) Exercise 10.37 (continued) Analysis: (continued) Exercise 10.38 Subject: Effect of intercooler location on the absorption of a light hydrocarbon mixture. Given: Feed gas and absorbent oil of Figure 10.17 of Example 10.4. Incooler with a duty of 500,000 Btu/h. Assumptions: SRK for K-values and enthalpies. Absorbent oil is nC12. Find: Effectiveness of the intercooler and its preferred location. Possible change in duty if intercooler stage temperature is at least 100oF. Analysis: The calculations of Example 10.4 were first repeated using the TOWER model of Chemcad. The following results differ from those of Example 10.4 because of the different methods used for computing K-values and enthalpies: Component C1 C2 C3 nC 4 nC 5 nC12 Total: Temp., oF lbmol/h: Feed gas 160.00 370.00 240.00 25.00 5.00 0.00 800.00 105 Absorbent 0.00 0.00 0.00 0.05 0.78 164.17 165.00 90 Gas out 146.25 268.83 96.41 1.11 0.21 0.15 512.96 144.9 Liquid out 13.75 101.17 143.59 23,94 5.57 164.02 452.04 144.4 Compared to results of Example 10.4, more is absorbed, but the temperature rise is less. For the effect of the intercooler, the calculations were also made with the Tower model (Insideout method) of Chemcad. The specifications for an intercooler of -500,000 Btu/h located at Stage 2 from the top were as follows, where it should be noted that the intercooler is treated as a feed between the absorbent and feed gas. No condenser Top pressure = 400 psia Column pressure drop = 0 psi. Number of stages = 6 Absorbent to stage 1 Intercooler with -0.500 MMBtu/h enthalpy (as a feed) at stage 2 Feed gas to stage 6 At the top, no condenser At the bottom, no reboiler Estimated distillate rate = 500 lbmol/h Estimated reflux rate = 200 lbmol/h Exercise 10.38 (continued) Analysis: (continued) Estimated temperature of stage 1 = 120oF Estimated temperature of bottom stage = 130oF Estimated temperature of stage 2 = 120oF Convergence was achieved in 6 iterations. The calculations were repeated for the intercooler located at stages 3, 4, and 5. The following results show that the outlet gas temperature was reduced and the amount of absorption was considerably increased, but the effect of stage location is not significant, although a location at stage 4 or 5 appeared to be very slightly best. Case Base - no intercooler (a) - intercooler stage 2 (b) - intercooler stage 3 (c) - intercooler stage 4 (d) -...
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