Short-Term Scheduling of Continuous Plants Based on Conditional Sequencing for Planned Maintenance

In this paper we present an extension of an earlier model for short-term scheduling of continuous/semicontinuous plants based on conditional sequencing, where a consumption task is conditionally aligned to a production task only if it receives material from production task; otherwise, if material is received from storage then sequencing is relaxed. Four-index binary and continuous variables are used to handle conditional sequencing by modifying the material balances and sequencing constraints in the earlier models. Two models with different timing variables are presented, and appropriate lower and upper bounds are postulated for different scenarios involving planned maintenance. The proposed models are demonstrated on different instances of a motivating example and on literature examples related to scheduling of continuous plants under planned maintenance operation, resulting in either improved objective function value and/or the converged solution is found using less number of events.