(80h) Optimal Scheduling of Multi-Product Pipeline Distribution with Consideration of Comprehensive Transmix Handling for Petroleum Refineries

Pipeline is more efficient and reliable to transfer large amounts of petroleum products than other ways via road, railroad, and vessel. To save capital and operating costs, one pipeline needs to transfer different types of oil products to different oil depots according to their ordinary demands. As two consecutive different types of oil products inside a pipeline will not be efficiently separated by a physical divider, the transmix (TM) will be generated in the interface between oil products. To guarantee the oil quality of product adopted by storage tanks at depots, a considerable amount of TM products along the pipeline needs to be handled properly. In reality, TMs can be handled by blending, distillation, or downgrading operations. Here, the downgrading operation means a TM mixed with similar types of oil products with different grades (e.g., premium and regular gasolines), could be considered as the lower-grade one (e.g., downgrade TMs mixed with premium and regular gasolines to the regular gasoline). The costs for blending and distillation comes from the storage, blending operation, transportation and reprocessing, while the cost for downgrading is a loss of margin which comes from the different price between the two mixed refined products. Thus, the objective function aiming at minimizing the total cost may ignore the potential benefit contributed by downgrading operations. Therefore, it is worth the effort to set the scheduling problem objective to maximize the total operating profit along the scheduling time horizon by optimizing the injection and transportation sequence as well as the transfer amounts of different oil products.

In this work, a new continuous-time based MILP model under the goal of maximizing the total operating profit is developed to optimize the distribution and inventory management of multiple oil products for petroleum refineries. The studied scope includes multiple refinery oil products, a long-distance pipeline, and several depots which consists of various storage tanks and transmix tanks dedicated to hold different pure products and TMs, respectively. The TM generated inside the pipeline will be handled with a combined method including blending, distillation, and downgrading operations. The TMs with different types of oil products (e.g., gasoline and diesel) will be handled by blending product-rich mixtures into pure products while recycling and distilling well-mixed TM portions. Meanwhile, the TMs mixed with similar types of oil products with different grades will be handled by downgrading operations. Overall, the scheduling model could provide optimal solutions including injection sequence and volume of oil product into pipeline, oil slugs movement inside pipeline, discharging product to multiple depot tanks, as well as exporting oil product based on the demands of consumer markets. The efficacy of the developed scheduling model has been demonstrated by multiple case studies.

Keywords: Multi-product, Scheduling, Pipeline, Transmix (TM), Blending, Distillation,

Downgrading, MILP, Maximizing profit