Scheduling of crude oil refinery operation with desalting as a separate task

A crude oil refining is a capital intensive process and releases a huge amount of environmentally unfriendly side-products. Scheduling of crude oil that determines the optimal unloading of crude from vessels to storages, transfer to blending tanks, and charging to distillation units (CDUs) in a way that minimizes the total operating cost has become the focus of the studies in the last few decades. In this paper, we present a model that extends the literature work of a unit-specific event-based model to incorporate desalting as a separate task and allows a desalting tank to feed multiple CDUs. The formulation is based on a state task network (STN) that uses a unit-specific event-based time representation. It considers different scenarios like simultaneous or sequential discharging of products and by-products from a desalting tank and whether a desalting tank feeding to multiple CDUs is allowed simultaneously or not. The proposed model leads a step closure to the reality and enables to know the amount of wash water needed, and the sludge disposed off for treatment in addition to the ordinary crude oil scheduling formulation. The performance of the proposed formulation is demonstrated using four case studies.