Scheduling of displacement batch digesters using discrete time formulation

Munawar A. Shaik, Shrikant Bhat

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


This paper provides mathematical programming based optimization model and computational results for short-term scheduling of displacement batch digesters in a pulp industry. The scheduling problem involves development of an optimal solution that yields the best sequence of operations in each of the parallel batch digesters sharing common resources. The constraints are imposed on meeting the demand of pulp of different qualities within a specified time horizon. The problem comprises of both fixed-time and variable time durations of the tasks, different storage policies, zero-wait and finite wait times, and handling of shared resources. The scheduling problem is formulated using a state-task-network (STN) representation of production recipes, based on discrete time representation resulting in a mixed-integer linear programming (MILP) problem which is solved using GAMS software. The basic framework is adapted from the discrete-time model of Kondili et al. (Comput. Chem. Eng., 1993, 17, 211-227). Different case studies involving parallel digesters in multiple production lines are considered to demonstrate the effectiveness of the proposed formulation using two different objective functions.

Original languageEnglish
Pages (from-to)318-339
Number of pages22
JournalChemical Engineering Research and Design
Issue number2
Publication statusPublished - Feb 2014
Externally publishedYes


  • Discrete-time representation
  • Displacement batch digesters
  • Optimization
  • Pulp industry
  • Scheduling
  • State-task-network representation

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering


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