(190o) Optimal Refinery Crude Scheduling with Considerations of Crude Mixing Along with the Pipeline Transportation

Front-end crude scheduling is a crucial issue for petroleum industries as the crude is transported through multi-stage facilities before entering crude distillation units (CDU), which normally include berth loading at port sites, various tanks for storage and blending, pipeline transportation, as well as CDU processing. Since the crude supply and consumption are subject to the more volatile market nowadays, the optimal crude scheduling becomes more increasingly important for the probability of refiners. The pipeline system is a vital transportation mode for petroleum industries due to its flexible operation, economic cost, high efficiency and low environmental impact. Distinguished from other transportation modes, like trucks and ships, the pipeline system is featured with continuous operations, thus it’s very suitable and economically beneficial for the transportation in large quantity and long distance. Therefore, it has been widely used for the transportation of crude oil, LNG, petroleum products and their derivatives.

The pipeline system is rarely considered in studies of crude scheduling. [1,2] Recently, some works are published incorporating the pipeline system into crude scheduling, which makes models more realistic.[3] However, these studies did not taken into account the crude mixing interface, the mixing at interface sections of two different types crudes. Usually, the crude mixing interface would generate a segment with combined properties of two mixed crudes. For crude refining, sulfur and heavy metal in crude oil are treated as key components, whose levels should be rigorously controlled before feeding CDUs. These key component concentrations in the mixed oil segment may cause off-spec oil properties inside charging tanks if their impacts are neglected, and thus jeopardize the CDU processing. For the safe and optimal operations of CDUs and the whole process, the crude mixing segment should be precisely identified together with the key component concentrations before the blending in the charging tanks and processing in the CDUs. Based on our literature survey, none published work has systematically addressed the oil mixing issues along with the pipeline transportation for refinery front-end crude scheduling.

In this study, a novel refinery crude scheduling model has been developed with the consideration of crude mixing along with the pipeline transportation, where the continuous-time representation is utilized to present the whole front-end crude movement scope. A detailed scheduling covering crude unloading from vessel, crude transportation through berths, storage tanks, pipeline system and charging tanks, and finally crude charging to CDUs is determined toward the maximal profit. In this work, CDUs with different requirements on key component concentrations are modeled and subject to manufacturing limits. Meanwhile, industrial operation constraints, such as multiple crude oils, crude blending and brine settling time, are taken into account to make the developed model more realistic and applicable in realities. In addition, some technical improvements on model, like the duration of tank holdup for inventory cost and the tighten bounds for transportation flowrate are also programmed to make model solution more practical. The efficacy and performance of the proposed model has been tested and demonstrated through various case studies.

References

[1] Lee, H., Pinto, J., Grossmann, I., & Park, S. (1996). Mixed-integer linear programming model for refinery short-term scheduling of crude oil unloading with inventory management. Industrial and Engineering Chemistry Research, 35(5), 1630–1641.

[2] Chen, X., Grossmann, I., Zheng, L., (2012)A comparative study of continuous-time models for scheduling of crude oil operations in inland refineries. Computer and Chemical Engineering, 44, 141-167

[3] Zhang, S., Xu, Q., (2015) Refinery continuous-time crude scheduling with consideration of long-distance pipeline transportation. Computer and Chemical Engineering, 75, 74-94.