Optimizing scheduling of refinery operations based on piecewise linear models

• A piecewise linear modeling approach is proposed to facilitate refinery scheduling.
• A unified partitioning strategy is designed for modeling multiple output variables.
• The piecewise linear model results in a mixed integer linear scheduling problem.
• The method is demonstrated on a Petro-SIM simulation of a real refinery in China.

Optimizing scheduling is an effective way to improve the profit of refineries; it usually requires accurate models to describe the complex and nonlinear refining processes. However, conventional nonlinear models will result in a complex mixed integer nonlinear programming (MINLP) problem for scheduling. This paper presents a piecewise linear (PWL) modeling approach, which can describe global nonlinearity with locally linear functions, to refinery scheduling. Specifically, a high level canonical PWL representation is adopted to give a simple yet effective partition of the domain of decision variables. Furthermore, a unified partitioning strategy is proposed to model multiple response functions defined on the same domain. Based on the proposed PWL partitioning and modeling strategy, the original MINLP can be replaced by mixed integer linear programming (MILP), which can be readily solved using standard optimization algorithms. The effectiveness of the proposed strategy is demonstrated by a case study originated from a refinery in China.