Computer aided distillation design

A computer assisted distillation design code has been developed for optimizing distillation columns with respect to minimizing total annual cost for certain binary and certain multicomponent systems. Two classes of binary systems are considered. The first class contains systems whose vapor-liquid equilibrium data can be characterized by a single, constant value of relative volatility. This approximation holds reasonably well for ideal mixtures. An example of a system considered which is approximately ideal is the Benzene-Toulene system. The second class of binary systems considered is that whose members exhibit an inflexion point when their vapor-liquid equilibrium data are plotted as composition in liquid and vapor phase. This behavior is somewhat representative of relatively highly non-ideal systems. An example of this kind of system is the aqueous solution of ethanol. The computer code in both cases is based on the McCabe-Thiele method of determining the number of theoretical plates required to produce a specified distillate/bottom split for a specified reflux ratio. The code for the system is developed to optimize the design based upon minimizing the total annual cost using cost data and the cost as a function of tower size curves provided by Peters and Timmerhaus. The optimization is done by establishing the optimum reflux ratio which yields the minimum total annual cost.

In the multicomponent case, the systems which are reasonably ideal, such as mixture of certain light hydrocarbons, are considered. The code is based upon the short cut method as presented by Treybal, and the published computer code of Chang. The task common to all the programs is the development of analytical equations which provide a reasonable fit to the property data, especially to the vapor-liquid equilibrium data of the systems. This task is accomplished by a published regression analysis routine.