Minimization of off-grade production in multisite multiproduct plants by solving multiple traveling salesman problem

András Király, Barbara Farsang, Tibor Chován, Maria Christidou, Evangelos Karlopoulos, János Abonyi

Research output: Contribution to journalConference article


Continuous multiproduct plants allow the production of several products (product grades). During grade transitions off-spec products are produced. The economic losses and the environmental impact of these transitions are sequence dependent, so the amount of off-grade products can be minimized by scheduling the sequence of the production of different products. Applying parallel production sites (m) increases the flexibility of multiproduct plants. Since market demands are changing, the production cycles of these sites should be re-scheduled in certain intervals. Therefore, our task is to design m production cycles that contains all required products by minimizing the total length of grade transitions. Most production scheduling problems such as the one considered in this paper are NP-hard. Our goal is to solve realistic problem instances in no more than a couple of minutes. We show that this problem can be considered as a multiple traveling salesmen problem (mTSP), where the distances between the products are based on the time or costs of the grade transitions. The resulted mTSP has been solved by multi-chromosome based genetic algorithm. The proposed algorithm was implemented in MATLAB and is available at the website of the authors ( For demonstration purposes, we present an illustrative example. The results show that multiproduct multisite scheduling problems can be effectively handled as mTSPs, and the proposed problem-specific representation based genetic algorithm can be used in wide range of optimization problems.

Original languageEnglish
Pages (from-to)1825-1830
Number of pages6
JournalChemical Engineering Transactions
Issue numberSpecial Issue
Publication statusPublished - Jan 1 2014
Event17th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction, PRES 2014 - Prague, Czech Republic
Duration: Aug 23 2014Aug 27 2014

ASJC Scopus subject areas

  • Chemical Engineering(all)

Fingerprint Dive into the research topics of 'Minimization of off-grade production in multisite multiproduct plants by solving multiple traveling salesman problem'. Together they form a unique fingerprint.

  • Cite this