Repeat Problems 10.D13 and 10.D13 using the two-enthalpy feed method in which a portion of the feed is condensed to a saturated liquid and the remainder is still a saturated vapor. Select the amount of feed to condense so that the column has pinch points at minimum reflux at both the liquid and the vapor feed simultaneously. Use the same multiplier, M, as in Problem 10.D13. Compare the diameter of this column to the diameter of \(10.27 \mathrm{ft}\) calculated for Problem 10.D9 and to the diameter calculated for Problem 10.D13. Calculate the ratio \(\mathrm{Q}_{\mathrm{R}, 2 \text {-enthalpy_feed }} / \mathrm{Q}_{\mathrm{R}, \text { vapor_feed }}\) for this problem.

Problems 10.D13

Repeat Problem 10.D9, calculating the diameter at the top, but condense the feed to a saturated liquid. Determine \((\mathrm{L} / \mathrm{D})_{\min }\) and \(\mathrm{L} / \mathrm{D}=\) \(1.43 \times(\mathrm{L} / \mathrm{D})_{\text {min }}\). Compare the diameter of this column to the diameter of \(10.27 \mathrm{ft}\) calculated for Problem 10.D9. Calculate the ratio \(Q_{R, \text { liquid_feed }} / Q_{R, \text { vapor_feed }}\) for this problem.

Problem 10.D9

Table 2-3

Table 2-8

D9.* 1000.0 kmol/h of a saturated vapor feed that is 60.0 mol% methanol and 40.0 mol% water is distilled in a sieve plate column operating at 75% of flooding velocity. Distillate is 99.9 mol% methanol, and bottoms is 1.0 mol% methanol. L/V = 0.6 and p = 1.0 atm. Use a 0.4572-m tray spacing and n = 0.90. Density of pure liquid methanol is 0.7914 g/ml. Data are available in Table 2-8 and Table 2-3. Assume an ideal gas. The surface tension of pure methanol can be estimated as = 24.0 - 0.0773 T with T in C (Dean, 1985, p. 10-110). . Calculate the diameter based on the conditions at the top of the column. Calculate (L/D) min and multiplier M = (L/D)/(L/D)min-