A process for the separation of a propylene propane mixture to produce 99 mol% propylene and 95 mol% propane is shown in Figure 10.34. Because of the high product purities and the low a, 200 stages may be required. A tray efficiency of 100% and tray spacing of 24 inches will necessitate two columns in series, because a single tower would be too tall. Assume a vapor distillate pressure of 280 psia, a pressure drop of 0.1 psi per tray, and a 2-psi drop through the condenser. The stage numbers and reflux ratio shown are only approximate. Determine the necessary reflux ratio for the stage numbers shown. Pay close attention to the determination of the proper feed-stage location so as to avoid pinch or near-pinch conditions wherein several adjacent trays may not be accomplishing any separation.

FEED 70F lbmol/h 1 atm. CH 360 1 CHg 240 CW 0 CW 2 COMPRESSOR 1 402.9 Hp 174F, 67 psia INTERCOOLER 598,200 Btu/h 120F, 65 psia COMPRESSOR 2 409.0 Hp 238F, 296 psia AFTERCOOLER 4,534,300 Btu/h 125.7F, 294 psia SURGE TANK FEED PUMP 2.5 Hp 100 62 PARTIAL REBOILER 32,362,000 Btu/h Stm PARTIAL CONDENSER 200 101 CW 30,700,000 Btu/h BOTTOMS 135.8F, 300 psia L/D = 15.9 VAPOR DISTILLATE 116F, 280 psia, Reflux drum INTERCOLUMN PUMP REFLUX PUMP 30 Hp 30 Hp Ibmol/h C3H 347.49 C3H8 3.51 Ibmol/h C3H6 12.51 CHg 236.49