Precedence-based Lot-sizing and Scheduling Formulation with Mixing/Splitting and Shared

PABLO A. MARCHETTI; JAIME CERDÁ

San Diego

Conferencia; 13th International Symposium on Process Systems Engineering (PSE 2018); 2018

PSE

In this work, a new multistage batch plant lot-sizing and scheduling formulation considering mixing and splitting operations at shared intermediate storage vessels is presented. The model relies on a batch-oriented general precedence representation that handles not only sequencing decisions at processing units but also intermediate storage time and capacity constraints. The proposed representation requires a predefined set of proposed batches for each product and processing stage. From these sets, selected batches are determined by the model through binary decisions. Batch integrity is not preserved but, instead, batches can be mixed/split between consecutive stages. The model includes allocation, timing, and sequencing variables and constraints similar to previous general precedence formulations. New binary variables are only added to handle material storage and transfer decisions, where both direct transfer and transfer through multiple storage vessels is supported. Besides, the general precedence sequencing binary variables are reutilized to also handle sequencing constraints at intermediate tanks. Time and capacity constraints for intermediate vessels are defined using the sequencing and material transfer binary decisions. Small/medium size examples are presented to illustrate the application of the model.