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Download fileOptimization Approaches for Efficient Crude Blending in Large Oil Refineries
journal contribution
posted on 2018-05-31, 00:00 authored by Jaime Cerdá, Pedro C. Pautasso, Diego C. CafaroTo
increase profit margin, refiners usually upgrade low cost crude
oils by mixing them with light crudes to obtain blends of higher value.
In recent years, this trend is favored by a shifting in the market
demand from gasoline toward diesel fuels that makes it more attractive
to process crude blends with higher diesel yields. Using in-line blending
stations, feedstocks for crude distillation units (CDUs) with the
desired properties are obtained by mixing flows of different types
of crude oils using the right blending recipe. In large oil refineries,
several CDUs are available to process a wide variety of crude oils
stored in many dedicated tanks. The scheduler must not only select
the cluster of tanks allocated to each CDU but also determine the
scheduling of the blending operations providing the best qualified
feedstocks for every distillation unit. Trace element compositions
and the temperature boiling point (TBP) curve are the properties normally
controlled to set the feedstock quality. In this work, two alternative
approaches are proposed to solve this challenging scheduling problem:
(a) an exact mixed-integer nonlinear (MINLP) formulation that simultaneously
considers tank allocation and operations scheduling decisions; (b)
an efficient sequential approach based on a pair of MINLP subproblems
making the tank allocation at the upper level and the scheduling decisions
at the lower one. After validation, the sequential approach is successfully
applied to new nine case studies involving up to four CDUs, 60 charging
tanks, and 14 types of crude oil.