SENSITIVITY OF DISTILLATION COLUMN DESIGN TO UNCERTAINTIES IN VAPOR-LIQUID-EQUILIBRIUM INFORMATION

The sensitivity of distillation column design [number of stages (N) an d reflux ratio (R)] to changes in the mean relative volatility (alpha) across the column is examined to demonstrate the effect that uncertai nties in the required vapor-liquid equilibrium (VLE) information has o n N and R. The results, presented in graphic form for different levels of alpha, provide the design engineer with a simple method of establi shing the required degree of accuracy in the VLE information used for a given separation. The sensitivity increases, as expected, with decre asing values of alpha, becoming very pronounced for difficult separati ons, but it is significant even for easier ones. Thus, for alpha = 1.1 , a 2% reduction in alpha leads to a 80% increase in N or an over 120% increase in R, while for alpha = 1.5 the corresponding increases are about 20 and 25%, respectively. The dependence of this sensitivity on design parameters, such as the ratio of the key components in the feed , feed thermal condition, etc., is also examined. The effect of the so urces of uncertainty in the VLE information: the values of the interac tion coefficient and, on occasion, of the critical properties and acen tric factor, is then demonstrated with two examples.