LP-based solution strategies for the optimal design of industrial water networks with multiple contaminants

This paper presents a new approach for the optimal design of water-using networks. Starting with a superstructure that accounts for all possible connections between water sources and water-using operations, different substructures are generated that consider all possible sequences of operations. Then, each operation is tackled one at a time, from the first to the last element in the sequence. This procedure has the advantage of replacing a nonlinear program (NLP) by a succession of linear programs (LP) that are solved for all operation sequences. Although part of the feasible region is lost in the process, the results have shown that the optimal solution is often obtained. The new procedure is at the same time a good approach of generating structurally different solutions that can be used as starting points for the full NLP. By doing this, local solutions can be avoided and the probability of finding the global optimal solution to the problem is increased. When compared to the standard initialization procedure that features a single starting point, the new approach is more efficient but substantially more demanding computationally. A trade-off can be reached by using the standard technique with multiple starting points originated from the possible operation sequences. (C) 2007 Elsevier Ltd. All rights reserved.