Sequential Initialisation Technique for Synthesising Multi- Period Multiple Utilities Heat Exchanger Networks

Abstract

This paper presents a new method for synthesizing heat exchanger networks involving multi-period operations and multiple utilities. Since process parameters, such as streams’ flowrate and supply/target temperatures, in multi-period operations usually fluctuate around some nominal conditions, the synthesis models developed for their optimisation need to ensure that the heat load requirement of every stream in every period of operation is satisfied. Solving problems of this nature is not a trivial task due to the presence of multiple periods of operations. The complexity is further compounded in situations where multiple options of utilities are involved in the optimisation task. Hence in this paper, a new synthesis method which involves firstly, solving single period models for each period of operation in the problem, after which the selected matches from each of the single period solution are systematically used to initialise the multi-period superstructure. Contrary to existing methods where utilities are placed or appended only in the first and last stage of the multi-period superstructure model, the newly presented method positions utilities in all stages of the superstructure where process streams of the opposite kind exist. The new approach is applied to two examples and the solutions obtained demonstrate the benefits of the method.