Minimum reflux calculations for nonideal mixtures using the reversible distillation model

A new approach for calculating minimum flows in simple distillation columns is presented. Unlike most previous work, no assumptions concerning ideal boiling or enthalpy behavior are required. The computation time is low, because neither rigorous simulation runs nor column iteration procedures are involved, and the method is suited for the evaluation of a large number of distillation sequences in terms of energy consumption at early stages of process design. The basic idea is the description of a distillation column under minimum reflux conditions by means of the reversible distillation model, which will be introduced briefly. The new method has been applied successfully to nonideal and azeotropic systems. Several calculations are illustrated with comparisons both to a rigorous and to the Underwood method. It will also be explained and demonstrated that the prediction and determination of tangent pinch points is a logical extension of the reversible distillation model.