Discrete-time and continuous-time scheduling approaches for crane-assisted pipeless process plants

Abstract

In pipeless process plants that employ cranes to transfer material-containing-vessels between equipment, scheduling of cranes along with the equipment-operations on vessels is crucial from a productivity perspective. The workings of such crane-assisted pipeless process plants can differ from each other depending on the nature of their set-ups and product(s) produced. For the scheduling of such plants which currently lack substantive research in the literature, it is important to explore and develop general methods, and the current work is an endeavor in this direction. Mixed integer linear programming (MILP) based models are developed in this work using the discrete-time and precedence-based continuous-time approaches. While the modeling using the discrete-time approach is developed from scratch, that based on the continuous-time approach is a continuation from our prior work (Aravind et al., 2021). We compare the two approaches and draw generic model-agnostic insights about the aptness of the approaches to suit the practical requirements of implementation, through computational studies. Modeling based on the continuous-time approach is found to be favored from a computational perspective despite its inherent complexity in construction.