'Costing' distillation systems from residue curve based designs

At present, when carrying out initial scoping of a project, one of the best ways to do preliminary designs for complicated separation systems is to us e residue curve maps. However, in order to compare the different possibilit ies one needs to do some preliminary costing. As one does not require very accurate costing at this stage, only wishing to eliminate expensive alterna tives, one would like to be able to do this directly from the sketches on t he residue curve maps. This paper presents methods by which this can be don e. In this paper we have limited ourselves to systems with constant relativ e volatilities, constant molar overflow and the differential equation descr iption of the distillation column. It is shown that, for the rectifying sec tion, by using binary approximations based on the least volatile component, one can obtain reasonable estimates (within a factor of two) for the numbe r of stages. This is done by noting that the changes in the least volatile component are the simplest in nature and using the sum of two binary approx imations as the final approximation. (C) 2000 Elsevier Science Ltd. All rig hts reserved.