Prediction of product distributions and vaporization efficiencies of distillation columns

Abstract

In an effort to simulate the separation of multicomponent mixtures on the plates of distillation columns, a new model for the plate efficiency was developed. This model is based in part on the condition of partial mixing in the liquid phase, and it is called the "Partially Mixed Model". In order to represent the composition of the vapor leaving a plate, a two point implicit formula is used. The weight factor μ in this formula is shown to be a measure of the degree of mixing. The model is shown to be very useful in the representation of the results of field tests which were made on commercial columns. From an analysis of the results of the field tests, μ was found to be strongly dependent upon the total flow rate of the reflux and the reflux ratio. A predictive method was developed for predicting the steady state solution at a given set of operating conditions from a known state solution at some other set of operating conditions. This predictive method is based on the fact that the θ method of convergence is an exact solution for certain total reflux problems. As demonstrated in the numerical examples, this new predictive method should be particularly useful in the feed-forward control of distillation columns and in the solution of optimization problems.