(662c) Multiperiod Planning of Refinery Operations under Market Uncertainty

A refinery contains a number of processes and various operations take place for turning raw material into higher value end products. The market demand drives the definition of the production targets (quantities of final products with specific properties within specified time periods) to a refinery. The steps for achieving these targets involve the processing of different crude oil on their own, or as a blend, in the distillation units. However, because of volatile raw material prices, fluctuating product demands, and other changing market conditions, many parameters in a planning/scheduling model are uncertain. One objective for oil operations in a refinery is to optimise the cost for crude oil inventories and product inventories. The current picture of the refining industry is characterised by stiff competition, stricter environmental regulations and heavier, sourer, costly crude oils, uncertainty in crude oil prices and uncertainty in the availability of the crude oil. Therefore, to maintain the profit margins in this ever-changing market environment, refiners need to have smarter operation strategies.

In any refinery operation planning sets targets for the scheduling operations and scheduling sets targets for advanced control whereas advanced control sends feedback to the scheduling and scheduling sends feedback to the planning model. For smooth operations, planning of the refinery operations under uncertainty is important in light of the ever changing market conditions. Thus, the consideration of uncertainty is interesting as it may create flexibility in the management decisions by exploiting the short term opportunities. The challenge is how to set optimal operating strategies to maximise the profit with satisfactory customer service levels.

This work presents a novel approach for the multiperiod planning of refinery operations under uncertainty. Considered problems involve uncertainty in product prices, and the crude oil purchase decisions along with refinery unit operations are optimised such that the overall profit for a refinery is maximised. In this multiperiod planning problem, the aim is to consider variation in product distribution during time horizon while considering the uncertainty in product prices and to provide appropriate operating strategy at different time points. The objective of multiperiod planning level optimisation is to provide good quality targets for the scheduling level. An oil refinery project has been evaluated when the prices of the product are uncertain and management has the flexibility to switch operating process units. For uncertainty in the product prices, normal distribution has been considered with given mean and standard deviation in the product prices. A case study has been carried out for the overall refinery plant optimistion, which includes an Atmospheric and Vacuum Distillation Unit (AVU), a Catalytic Reforming Unit (CRU), a Residue Fluid Catalytic Cracking Unit (RFCCU), a Delayed Coking Unit (DCU), several hydrotreating units, product blending units and auxiliary units. The results of the case study demonstrate that the flexibility model helps the optimizer to find better optima.