D. Problems * Answers to problems with an asterisk are at the back of the book. 01. Repeat Example 10-1 for an average column pressure of 700.0 kPa. 10 a - EXAMPLE 10-1. Overall efficiency estimation EXAMPLE A sieve plate distillation column is separating a feed that is 50.0 mol% n-hexane and 50.0 mol% n-heptane. The feed is a saturated liquid. Plate spacing is 24.0 in. Average column pressure is 1.0 atm. Distillate composition is xp = 0.999 (mole fraction n-hexane) and Xo = 0.001. The feed rate is 1000.0 lbmol/h. The internal reflux ratio L/V = 0.8. The column has a total reboiler and a total condenser. Estimate the overall efficiency. Solution To use the O'Connell correlation we need to estimate a and u at feed composi- tion and the average temperature and pressure of the column. Column tempera- ture can be estimated from equilibrium (De Priester chart). The following values are generated from Figure 2-12: Xc6 0.0 0.0 T, C 98.4 0.341 0.398 0.545 0.609 85.0 83.7 0.50 0.70 80.0 1.0 1.0 69.0 Relative volatility is a = (y/x)[(1 - y)/(1 - x)]. The average temperature can be estimated several ways: Arithmetic average T = (98.4 + 69.0)/2.0 = 83.7. a. = 2.36 Average at x = 0.5, T = 80.0, 0 = 2.33 Not much difference. Use a = 2.35 corresponding to approximately 82.5C