Optimal scheduling of single stage batch plants with direct heat integration

•We address energy efficiency in a vegetable oil refinery.•A mathematical model is proposed to reduce utility consumption.•Key aspect is to ensure synchronization of hot and cold streams.•Energy savings may be doubled if production is delayed.•Savings up to 40% can be achieved.

This paper addresses the multi-objective optimization problem arising in the operation of heat integrated batch plants, where makespan and utility consumption are the two conflicting objectives. A new continuous-time MILP formulation with general precedence variables is proposed to simultaneously handle decisions related to timing, product sequencing, heat exchanger matches (selected from a two-stage superstructure) and their heat loads. It features a complex set of timing constraints to synchronize heating and cooling tasks, derived from Generalized Disjunctive Programming. Through the solution of an industrial case study from a vegetable oil refinery, we show that major savings in utilities can be achieved while generating the set of Pareto optimal solutions through the ɛ-constraint method.