Synthesis of combined heat and reactive mass-exchange networks

Abstract

In this work we introduce the problem of synthesizing combined heat and reactive mass exchange networks “CHARMENs”. The synthesis task involves the preferential transfer of a certain species from a set of rich streams to a set of lean streams and at the same time accomplish a specified heat transfer task in a cost effective manner. The economic objectives of mass exchange and heat recovery are in general incompatible and need to be addressed simultaneously. The proposed work introduces a systematic and generally applicable procedure to trade-off the two objectives and synthesize a CHARMEN. First, we derive a number of important properties of the problem. Based on these characteristics, a two-stage targeting procedure is developed. In the first stage, the minimum operating cost “MOC” of the network is identified via a mixed-integer nonlinear program “MINLP”. A shortcut linear formulation is also devised to identify a near-optimum MOC solution which may be used as an initial guess for the MINLP. The optimum solution to the MOC problem results in a natural decomposition of the original CHARMEN problem into two independent subproblems that may be solved to identify the minimum number of heat and reactive mass exchangers. The applicability of the synthesis procedure is demonstrated by tackling a case study on the desulfurization of gaseous wastes with simultaneous heat recovery.