Optimal scheduling of continuous plants with energy constraints

Pedro M. Castro*, Iiro Harjunkoski, Ignacio E. Grossmann

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

63 Citations (Scopus)


This work addresses the scheduling of continuous single stage multiproduct plants with parallel units and shared storage tanks. Processing tasks are energy intensive and we consider time-dependent electricity pricing and availability together with multiple intermediate due dates, handled as hard constraints. A new discrete-time aggregate formulation is proposed to rapidly plan the production levels. It is combined with a continuous-time model for detailed scheduling as the essential part of a rolling-horizon algorithm. Their computational performance is compared to traditional discrete and continuous-time full-space formulations with all models relying on the Resource-Task Network (RTN) process representation. The results show that the new models and algorithm can generate global optimal schedules much more efficiently than their counterparts in problems involving unlimited power availability. Under restricted power, the aggregate model underestimates the electricity cost, which may cause the rolling-horizon approach to converge to a suboptimal solution, becoming the discrete-time model a better approach.

Original languageEnglish
Pages (from-to)372-387
Number of pages16
JournalComputers and Chemical Engineering
Issue number2
Publication statusPublished - 9 Feb 2011
MoE publication typeA1 Journal article-refereed


  • Continuous-time model
  • Mixed-integer linear programming
  • Non-uniform time grid
  • Production planning
  • Resource-Task Network


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