Unit-specific event based continuous-time formulation for scheduling hybrid process

The hybrid production process here includes batch and continuous production modes where batch process is composed of several parallel reactors, and the continuous process is one or few continuous production line. Between the two processes, there is intermediate storage tank with limited capacity. The task of the scheduling is to coordinate batch reactors, intermediate storage and continuous production line in order to avoid wait of semi-finished product in reactors, and guarantee the smooth production of back continuous production line. Based on unit-specific event based continuous-time modeling method, this paper presents a novel mixed integer nonlinear programming (MINLP) formulation for scheduling the whole hybrid process where the objective is to minimize makespan and some practical constraints are considered, such as limitations on batch-size, processing time dependent on batch-size, finite intermediate storage, demand etc. Some valid cuts are derived and introduced to the model for improving the computational performance. The performance of the model is illustrated by some real case studies, and its efficiency and limitation are also analyzed for its future real application.