A multitasking continuous time formulation for short-term scheduling of operations in multipurpose plants

Short-term scheduling in multipurpose batch plants has received significant attention in the past two decades. Both discrete-time and continuous time formulations have been proposed to model the problem; however, multipurpose plants that have machines with the ability to process multiple tasks at the same time, i.e. multitasking, have been overlooked by the available continuous time formulations in the literature. This paper presents a novel MILP formulation that is capable of accommodating the multitasking feature in the machines of a facility. The performance of the presented formulation is studied in comparison with a single-tasking formulation. The results show that, while the multitasking formulation is not more costly in terms of solution time, it is capable of producing significantly better solutions. The presented formulation takes into account several other operational constraints of multipurpose facilities and can be readily applied to facilities that have machines capable of multitasking, including plants in the analytical services sector.