Chemical Engineering Science, Vol.84, 197-206, 2012
Enhanced nearest neighbors algorithm for design of water networks
The Nearest Neighbors Algorithm (NNA) provides a reliable synthesis tool for systematically designing water networks involving fixed flowrate (FF) operations. The Enhanced NNA in this work extends the applicability of the algorithm to fixed contaminant-load (FC) operations by giving priority to local-recycle (LR) matches. The flowrate of the LR match is maximized by choosing the neighbor source as the cleanest available source rather than the nearest neighbor. Subsequently, the LR matches are eliminated for FC operations to yield relatively simple network designs that not only satisfy the minimum freshwater target but also minimize the water flowing through the process units resulting in reduced network cost. The flowrate calculation for neighbor sources in the Enhanced NNA is simplified requiring mere substitution in formulae rather than the earlier simultaneous solution of flow and load balance equations. Case studies are presented to illustrate the versatility of the Enhanced NNA in generating multiple optimum network designs, handling hybrid water network problems where both FF and FC operations coexist, and designing superior practical networks with regeneration including zero wastewater discharge. (C) 2012 Elsevier Ltd. All rights reserved.