DETERMINE THE MINIMUM TRAY REQUIREMENT Nmin o Calculate Nmin using the fenske equation As a rule of thumb, the column height should not exceed 30 m Normal tray spacing is 2 ft 0.6m Thus the maximum number of trays we can have is about 50 trays As another rule of thumb the number theoretical trays should be about 1.5 Nmin to 2.0 Nmin. So, if Nmin>30, the column height guideline will probably be exceeded if so, either E adjust the separation specs(if possible) accept the additional height requirement,or go to a different separation, e.g. extractive distillate 9/2799 Simple distillation design9/27/99 Simple Distillation Design 7 DETERMINE THE MINIMUM TRAY REQUIREMENT Nmin u Calculate Nmin using the Fenske Equation u As a rule of thumb, the column height should not exceed 30 m. Normal tray spacing is 2 ft or 0.6 m. Thus the maximum number of trays we can have is about 50 trays u As another rule of thumb, the number theoretical trays should be about 1.5 Nmin to 2.0 Nmin. So, if Nmin > 30, the column height guideline will probably be exceeded u If so, either ð adjust the separation specs (if possible) ð accept the additional height requirement, or ð go to a different separation, e.g. extractive distillation