Numerical Calculation of Separation Processes

Abstract

Distillation is one of the most common separation processes carried out in industry. Separation by distillation is based on the different volatilities of the components of a mixture. If a liquid mixture of two or more components is partially vaporized or if a vapor mixture is partially condensed, then, in either case, the vapor product is richer in the component of highest volatility while the liquid product is richer in the component of lowest volatility. A one-stage vaporisation or condensation process gives products of a certain limited purity. In order to increase product purity, a sequence of successive vaporizations of the liquid products, resp. a sequence of successive condensations of the vapor products, are used. An economic way for carrying out such a multistage distillation process is a distillation column, see Fig. 1. The column consists of a number of plates, on each of which vapor and liquid are in equilibrium with each other. The mixture enters the column at some plate (feed). Under the force of gravity the liquid flows downwards. A heater, called the reboiler, at the bottom of the column vaporizes a portion of the liquid. The resulting vapor flows upwards. A condensor at the top of the column liquifies a portion of vapor which is returned to the column (reflux). The remaining portion of the overhead vapor is called the distillate.