Although the largest errors in calculating the height of a packed column are errors in (1) mass transfer coefficients and (2) VLE data, calculation errors can also be significant because calculation of \(n_{G}\) and \(\mathrm{n}_{\mathrm{OG}}\) both require subtracting \(\mathrm{y}\) values that are close to each other and taking the inverse of this difference. Suppose that all values of \(\mathrm{y}_{\mathrm{AI}}-\) \(\mathrm{y}_{\mathrm{A}}\) in the table in Example 16-1 are too low by 0.001 (thus, for \(\mathrm{y}_{\mathrm{A}}=\) 0.8 the value of \(\mathrm{y}_{\mathrm{AI}}-\mathrm{y}_{\mathrm{A}}\) should be 0.013 ). Recalculate the area for \(\mathrm{n}_{\mathrm{G}, \text { enriching }}\) and the required height of packing in the enriching section.

Example 16-1

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Repeat Example 4-3 (distillation of ethanol and water) except using a column packed with 2.0- in. metal Pall rings. F = 1000.0 kmol/h, z = 0.20, Tp = 80.0F, xp = 0.80, xg = 0.02, L/D = 5/3, and p = 1.0 atm. Use a vapor flow rate that is nominally 75% of flooding. In the enriching section HG = 0.4054 m and H = 0.253 m, and in the stripping section HG = 0.2835 m and H = 0.1067 m (determined in Example 16-2). Example 4-3 A distillation column with a total condenser and a partial reboiler is separating an ethanol- water mixture. Feed is 20 mol% ethanol, feed rate is 1000 kmol/h, and feed temperature is 80F. Distillate is 80 mol% ethanol, and bottoms is 2 mol% ethanol. External reflux ratio is 5/3. Reflux is a saturated liquid, and CMO can be assumed. Pressure is 1 atm. Find optimum feed plate location as stages above the reboiler and total number of equilibrium stages. Example 16-2 Estimate values of HG and H for the distillation in Examples 4-3 and 16-1 using 2.0-in. metal Pall rings.