Improving the Computational Performance of STN/RTN Formulations for Short-Term Scheduling

GUILLERMO A. DURAND; J. ALBERTO BANDONI

INDUSTRIAL & ENGINEERING CHEMICAL RESEARCH

American Chemical Society Publications

Año: 2010 vol. 49 p. 12477 - 12495

0888-5885

In this article, we present a series of integer cuts to improve the computational performance of scheduling problems based on either discrete- or continuous-time representation. They are expressed as novel equations in terms of binary variables alone that take advantage of structural characteristic of general STN and RTN formulations. Different fixed pairs of tasks appearing in scheduling problems of continuous and batch-continuous processes are identified, and corresponding integer cuts are developed to improve the solution efficiency of the mathematical formulations. For demonstration purposes, five selected scheduling formulations are modified as proposed in this article and applied to three well-known benchmark problems, and their computational performances are compared against the unmodified formulations. An industrial case study is also used to demonstrate the advantages of using the new equations. This case study corresponds to a sector, the so-called “sugarhouse”, of a beet sugar plant. The scheduling model is presented, and the results are discussed in terms of both the optimal plant schedule and the computational point of view.