(708f) Simultaneous Scheduling for Refinery Plant Manufacturing and Downstream Multi-Product Pipeline Distribution

Refinery manufacturing and oil product distribution systems are highly correlated in the entire refinery supply chain. If they were handled separately, it may cause imbalances or discrepancies between the production and distribution sectors, and thus the loss of the profit margin across the refinery supply chain. On the contrary, the optimal coordination between these two systems could benefit not only the industrial profitability, but also the reduction of both management risks. Many published studies have addressed refinery production and pipeline distribution system separately, while only a few works have addressed two sectors simultaneously. Existing publications either focused on the strategic and tactical decision level for the upstream and midstream (Azadeh et al., 2017), or simply considered the scheduling problem with a discrete framework (Guyonnet et al., 2009, Tong et al., 2012). However, there is still lack of the systematic and integrated study dealing with the continuous-time and continuous-slug based scheduling problem with long-distance pipeline transportations.

For the multi-product pipeline distribution part, 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 of two different kinds of products. To guarantee the oil quality of product adopted by storage tanks at depots, a considerable amount of TM products from the pipeline needs to be handled properly at depots. In reality, TMs can be handled by blending, distillation, and 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). Conceivably, the multi-product pipeline scheduling problem with consideration of handling with TM inside the pipeline present a big challenge to oil industries. There are few works reported in this topic (e.g., Rejowski et al. (2003); Cafaro and Cerdá (2004 and 2010)). However, there are still lack of studies on dealing with the TM by a comprehensive method including blending, distillation and downgrading operations.

In this work, a new continuous-time based integrated MINLP model is developed to optimize the scheduling of both refinery manufacturing operation and multi-product pipeline distribution by handling TMs with a comprehensive method including blending, distillation and downgrading operations. The scheduling objective is to maximize the total plant profit; meanwhile, operation rules and product specifications, inventory limits, delivery constraints and oil product demands must be satisfied. The scope of this work contains two main parts: a refinery plant and a long-distance pipeline distribution system connecting refinery oil products to multiple depots. The refinery includes crude distillation, reforming, cracking, hydrotreating, blending, gas processing, and sulfur recovering facilities. The long-distance pipeline distribution system connecting the refinery tank farm and multiple depots, which transport oil products to different local markets. Each depot consists of storage tanks and transmix tanks dedicated to hold pure product and TM, respectively. The TM generated inside the pipeline will be handled with a combined method of blending, distillation and downgrading. The TM with different types (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 integrated simultaneously scheduling model could provide optimal solutions such as processing stream property and flowrate for unit operations, yield and inventory of various petrochemical products, oil slugs movement inside pipeline, as well as oil product discharging to multiple depot tanks based on consumer demands. The efficacy of the developed integrated scheduling model is demonstrated by an industrial scale study.

Keywords: Simultaneous scheduling, Refinery manufacturing, Multi-product, Pipeline, Transmix, Blending, Distillation, Downgrading, MINLP

References

Azadeh, A., Shafiee, F., Yazdanparast, R., Heydari J., and Keshvarparast, A. (2017). Optimum Integrated Design of Crude Oil Supply Chain by a Unique Mixed Integer Nonlinear Programming Model. Industrial & Engineering Chemistry Research, 56: 5734−5746.

Guyonnet, P., Grant, F.H., Bagajewicz, M.J. (2009). Integrated Model for Refinery Planning, Oil Procuring, and Product Distribution. Industrial & Engineering Chemistry Research, 48: 463–482.

Tong, K., Feng, Y., Rong, G. (2012). Integrated Model for Refinery Production and Pipeline System Scheduling. Proceedings of the 22nd European Symposium on Computer Aided Process Engineering, 17 - 20 June 2012, London.

Cafaro, D., & Cerdá, J. (2004). Optimal scheduling of multiproduct pipeline systems using a non-discrete MILP formulation. Computers and Chemical Engineering, 28, 2053–2068. ISSN 0098-1354.

Cafaro, D., & Cerdá, J. (2010). Operational scheduling of refined products pipeline networks with simultaneous batch injections. Computers and Chemical Engineering, 34, 1687–1704.

Rejowski, R., & Pinto, J. (2003). Scheduling of a multiproduct pipeline system. Com- puters and Chemical Engineering, 27, 1229–1268.