MULTICOMPONENT DISTILLATION Calculation （多组分精馏计算 ）.pdf

Chapter 2 Shortcut or approximate calculation methods MULTICOMPONENT DISTILLATION Calculation 飦 Shortcut or approximate calculation methods 飦 Rigorous calculation or plate to plate methods Light key heavy key 飦 Light key component: present in the residue in important amounts while components lighter than the light key are present in only very small amounts 飦 Heavy key component: present in the distillate in important amounts while components heavier than the heavy key are present in only very small amounts Total reflux calculation 飦 飦 Example 2-1 by Treybal The following feed at 82 C ,1035 kN/m2 is to be fractionated at that pressure so that the vapor distillate contains 98% of the C H but only 1% of the C H 3 8 5 12 Compute the number of theoretical trays at total reflux and the corresponding products Solution Assume distillate temperature 46 C residue temperature 114 C Solution For C 4: A C balance: 4 Solving simultaneously gives Solution similarly Therefore at total reflux Solution The distillate dew point computes to be 46.3C the residue bubble point 113 C. The assumed 46 114 C are close enough. Example 2-2 by Van Winkle The following feed is available at its bubble point at 100 psia and it is to be fractionated to produce a residue containing 95% of the isobutane in the feed and the composition with respect to propane not more than 0.1 mol%.Determine minimum plates at total reflux by the Fenske method. Use K Values from Fig 2.41. Solution The material balance is fixed by the specifications on the bottoms (constant vapor and liquid enthalpics are assumed in this example). b