Single and multi-objective optimisation for the retrofit of process water networks

Jui Yuan Lee, Chung Hsuan Tsai, Dominic Chwan Yee Foo

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


This work develops a generic mathematical model for process engineers and designers to retrofit existing water networks in process plants for water savings. The model is applicable to both direct reuse/recycling and regeneration schemes, with single- and multi-objective optimisation scenarios. The objectives of the model may include minimum water flowrates, minimum extent of retrofits and/or a reasonable payback period. A literature case study involving an existing water network in a pulp and paper mill is solved to elucidate the newly proposed model. The results of single-objective optimisation show maximum annual cost savings of $4,027,919 in the direct reuse/recycling scheme (with a 57.2% freshwater saving) and $4,420,975 in the regeneration scheme (with an 84.5% freshwater saving). For multi-objective optimisation, the use of the constraint method in the direct reuse/recycling scheme generates a range of Pareto optimal solutions for selection by the decision-maker. It was found that 88.1% of the freshwater saving can be achieved with 44.2% of the piping retrofit cost. Although the compromise solution obtained using fuzzy optimisation in the regeneration scheme achieves only 66.6% of the freshwater saving with 86% of the total retrofit cost, the number of new and modified connections is reduced by more than half.

Original languageEnglish
Pages (from-to)39-47
Number of pages9
JournalJournal of the Taiwan Institute of Chemical Engineers
Publication statusPublished - 2020 Dec

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Chemical Engineering


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